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