Today it worked. I am back to Volla. I did the same, but less error messages, the links worked.

@applee

Funny, it was my first attempt to flash lineage 18 with the tools you mentioned, but i failed. So I was glad that it worked with the UBport installer to get a working UT.

I hope they will renew the certificate or I will wait until the version 0.9.

@applee
Hi applee,
doesn´t work:
warning security risk - foreward - password needed

;-(

Installing UT on an Volla Phone worked fine with the UBports linux installer 0.8.8. But there is no way back to Volla OS or to Sailfish.
Error message (Volla):
core:download: Error: core:download Error: Error: Download Error: https://ota.volla.tech/builds/volla-9.0-20201019-nightly-k63v2_64_bsp-signed.zip
Error [ERR_TLS_CERT_ALTNAME_INVALID]: Hostname/IP does not match certificate's altnames: Host: ota.volla.tech. is not in the cert's altnames: DNS:volla.tech

Error message (Sailfish):
Error: core:download: Error: core:download Error: Error: Download Error: https://gitlab.com/sailfishos-porters-ci/yggdrasil-ci/-/jobs/artifacts/master/download?job=run-build-lvm Error: ENOENT: no such file or directory, open 'C:\Users\ich-del\AppData\Roaming\ubports\yggdrasil\SailfishOS\download?job=run-build-lvm'
ignore - internetconnection lost
Error: core:unpack: Error: Exited with code 7