@Eric-H It worked

It was my fault — I had skipped that step because I thought it was impossible to downgrade the OS version.

But it was actually straightforward to just execute the flash_all.sh.

Thank you so much!

During the installation of Ubuntu Touch with the UBports Installer I hit this error:

error: Error: fastboot:flash: Error: Flashing failed: {"error":{"code":1},"stderr":"FAILED (remote: 'Partition not found')fastboot: error: Command failed"}
stack trace: Error: Flashing failed: {"error":{"code":1},"stderr":"FAILED (remote: 'Partition not found')fastboot: error: Command failed"}

Detailed context:

$ fastboot getvar all
(bootloader) DP:0x0
(bootloader) token:VQEBHwEQF_qzQcIU3FNd0uobubiIEgMFc3VyeWECBJZjiyU
(bootloader) parallel-download-flash:yes
(bootloader) hw-revision:10000
(bootloader) unlocked:yes
(bootloader) off-mode-charge:1
(bootloader) charger-screen-enabled:1
(bootloader) battery-soc-ok:yes
(bootloader) battery-voltage:3656
(bootloader) version-baseband:
(bootloader) version-bootloader:
(bootloader) erase-block-size: 0x1000
(bootloader) logical-block-size: 0x1000
(bootloader) variant:SM7 UFS
(bootloader) partition-type:fsc:raw
(bootloader) partition-size:fsc: 0x20000
(bootloader) partition-type:fsg:raw
(bootloader) partition-size:fsg: 0xA00000
(bootloader) partition-type:modemst2:raw
(bootloader) partition-size:modemst2: 0x200000
(bootloader) partition-type:modemst1:raw
(bootloader) partition-size:modemst1: 0x200000
(bootloader) partition-type:ALIGN_TO_128K_2:raw
(bootloader) partition-size:ALIGN_TO_128K_2: 0x1A000
(bootloader) partition-type:dtbo:raw
(bootloader) partition-size:dtbo: 0x1800000
(bootloader) partition-type:boot:raw
(bootloader) partition-size:boot: 0x8000000
(bootloader) partition-type:vbmeta:raw
(bootloader) partition-size:vbmeta: 0x10000
(bootloader) partition-type:catecontentfv:raw
(bootloader) partition-size:catecontentfv: 0x100000
(bootloader) partition-type:catefv:raw
(bootloader) partition-size:catefv: 0x80000
(bootloader) partition-type:secdata:raw
(bootloader) partition-size:secdata: 0x7000
(bootloader) partition-type:uefivarstore:raw
(bootloader) partition-size:uefivarstore: 0x80000
(bootloader) partition-type:multiimgqti:raw
(bootloader) partition-size:multiimgqti: 0x8000
(bootloader) partition-type:multiimgoem:raw
(bootloader) partition-size:multiimgoem: 0x8000
(bootloader) partition-type:storsec:raw
(bootloader) partition-size:storsec: 0x20000
(bootloader) partition-type:logdump:raw
(bootloader) partition-size:logdump: 0x4000000
(bootloader) partition-type:cateloader:raw
(bootloader) partition-size:cateloader: 0x200000
(bootloader) partition-type:logfs:raw
(bootloader) partition-size:logfs: 0x800000
(bootloader) partition-type:toolsfv:raw
(bootloader) partition-size:toolsfv: 0x100000
(bootloader) partition-type:limits:raw
(bootloader) partition-size:limits: 0x1000
(bootloader) partition-type:splash:raw
(bootloader) partition-size:splash: 0x20A4000
(bootloader) partition-type:spunvm:raw
(bootloader) partition-size:spunvm: 0x800000
(bootloader) partition-type:apdp:raw
(bootloader) partition-size:apdp: 0x40000
(bootloader) partition-type:dip:raw
(bootloader) partition-size:dip: 0x100000
(bootloader) partition-type:devinfo:raw
(bootloader) partition-size:devinfo: 0x1000
(bootloader) partition-type:uefisecappbak:raw
(bootloader) partition-size:uefisecappbak: 0x200000
(bootloader) partition-type:imagefvbak:raw
(bootloader) partition-size:imagefvbak: 0x200000
(bootloader) partition-type:cmnlib64bak:raw
(bootloader) partition-size:cmnlib64bak: 0x80000
(bootloader) partition-type:cmnlibbak:raw
(bootloader) partition-size:cmnlibbak: 0x80000
(bootloader) partition-type:keymasterbak:raw
(bootloader) partition-size:keymasterbak: 0x80000
(bootloader) partition-type:ablbak:raw
(bootloader) partition-size:ablbak: 0x800000
(bootloader) partition-type:mdtpbak:raw
(bootloader) partition-size:mdtpbak: 0x2000000
(bootloader) partition-type:mdtpsecappbak:raw
(bootloader) partition-size:mdtpsecappbak: 0x400000
(bootloader) partition-type:hypbak:raw
(bootloader) partition-size:hypbak: 0x80000
(bootloader) partition-type:tzbak:raw
(bootloader) partition-size:tzbak: 0x400000
(bootloader) partition-type:aopbak:raw
(bootloader) partition-size:aopbak: 0x80000
(bootloader) partition-type:uefisecapp:raw
(bootloader) partition-size:uefisecapp: 0x200000
(bootloader) partition-type:imagefv:raw
(bootloader) partition-size:imagefv: 0x200000
(bootloader) partition-type:qupfw:raw
(bootloader) partition-size:qupfw: 0x10000
(bootloader) partition-type:devcfg:raw
(bootloader) partition-size:devcfg: 0x20000
(bootloader) partition-type:cmnlib64:raw
(bootloader) partition-size:cmnlib64: 0x80000
(bootloader) partition-type:cmnlib:raw
(bootloader) partition-size:cmnlib: 0x80000
(bootloader) partition-type:keymaster:raw
(bootloader) partition-size:keymaster: 0x80000
(bootloader) partition-type:dsp:raw
(bootloader) partition-size:dsp: 0x2000000
(bootloader) partition-type:abl:raw
(bootloader) partition-size:abl: 0x800000
(bootloader) partition-type:mdtp:raw
(bootloader) partition-size:mdtp: 0x2000000
(bootloader) partition-type:mdtpsecapp:raw
(bootloader) partition-size:mdtpsecapp: 0x400000
(bootloader) partition-type:bluetooth:raw
(bootloader) partition-size:bluetooth: 0x100000
(bootloader) partition-type:modem:raw
(bootloader) partition-size:modem: 0x10000000
(bootloader) partition-type:hyp:raw
(bootloader) partition-size:hyp: 0x80000
(bootloader) partition-type:tz:raw
(bootloader) partition-size:tz: 0x400000
(bootloader) partition-type:aop:raw
(bootloader) partition-size:aop: 0x80000
(bootloader) partition-type:ddr:raw
(bootloader) partition-size:ddr: 0x100000
(bootloader) partition-type:cdt:raw
(bootloader) partition-size:cdt: 0x20000
(bootloader) partition-type:ALIGN_TO_128K_1:raw
(bootloader) partition-size:ALIGN_TO_128K_1: 0x1A000
(bootloader) partition-type:xbl_configbak:raw
(bootloader) partition-size:xbl_configbak: 0x20000
(bootloader) partition-type:xblbak:raw
(bootloader) partition-size:xblbak: 0x700000
(bootloader) partition-type:xbl_config:raw
(bootloader) partition-size:xbl_config: 0x20000
(bootloader) partition-type:xbl:raw
(bootloader) partition-size:xbl: 0x700000
(bootloader) partition-type:userdata:ext4
(bootloader) partition-size:userdata: 0x1A34DE3000
(bootloader) partition-type:super:raw
(bootloader) partition-size:super: 0x200000000
(bootloader) partition-type:ffu:raw
(bootloader) partition-size:ffu: 0x800000
(bootloader) partition-type:gsort:raw
(bootloader) partition-size:gsort: 0x1000000
(bootloader) partition-type:exaid:raw
(bootloader) partition-size:exaid: 0x18000000
(bootloader) partition-type:cache:ext4
(bootloader) partition-size:cache: 0x18000000
(bootloader) partition-type:metadata:ext4
(bootloader) partition-size:metadata: 0x1000000
(bootloader) partition-type:vbmeta_system:raw
(bootloader) partition-size:vbmeta_system: 0x10000
(bootloader) partition-type:recovery:raw
(bootloader) partition-size:recovery: 0x8000000
(bootloader) partition-type:cust:raw
(bootloader) partition-size:cust: 0x40000000
(bootloader) partition-type:minidump:raw
(bootloader) partition-size:minidump: 0x8000000
(bootloader) partition-type:frp:raw
(bootloader) partition-size:frp: 0x80000
(bootloader) partition-type:keystore:raw
(bootloader) partition-size:keystore: 0x80000
(bootloader) partition-type:misc:raw
(bootloader) partition-size:misc: 0x100000
(bootloader) partition-type:persist:raw
(bootloader) partition-size:persist: 0x2000000
(bootloader) partition-type:ssd:raw
(bootloader) partition-size:ssd: 0x2000
(bootloader) secure:yes
(bootloader) serialno:3a962018
(bootloader) cpuid:0x96638b25
(bootloader) anti:2
(bootloader) product:surya
(bootloader) is-userspace:no
(bootloader) max-download-size:805306368
(bootloader) kernel:uefi
all:
Finished. Total time: 0.010s