Not booting after failed update to OTA-8

[jilly]

After trying to install OTA-8 on Fairphone 4 and failing with a message similar to "No space left on partition" my fairphone keeps getting stuck at the "Fairphone Powered by Android" screen.
The boot loader warning ("The boot loader is unlocked and software integrity cannot be guaranteed..." and so on) shows, then the "Fairphone Powered by Android" screen shows and nothing else happens.
Before the botched install, I had UT 20.04 stable OTA-7 installed on the phone.
I started the botched OTA-8 install from within the phone's Ubuntu Touch settings app.
I tried fixing the installation with the phone connected via USB to my computer with the UBports Installer, but it does not get past "Waiting for device... Fastboot is scanning for devices".
I tried running

adb devices

and my device is listed. Afterwards I ran

adb reboot bootloader

but it fails with the message

reboot (reboot,bootloader) failed

Now I am hoping for any pointers on what else I could try. Thanks in advance

[jilly]

I was able to boot into bootloader by long pressing power + volume up buttons on the Fairphone. Afterwards UBports installer was able to find the device and install UT OTA-8.
So everything runs fine again. Thanks so much