I found option of rollbacks in the documentation, so I was able to fix it by doing the rollback.
To anyone who has same issue, follow rollback instructions here: Schnapps - Turris Documentation
I have SD card plugged-in and I do not think, that you have to connect to specific port. I connected via configured IP, not default one.
Maybe try reboot your router first by unplugging the cable.
My Omnia updated from Turris version 5.4.4 to 6.0 (Linux kernel 4.14 to 5.15) either last night or this morning, I didn’t check.
In any case, it did not reboot automatically, the mail announced it would do so soon.
But its outside connection was unstable, I lost both data (internet) and phone connectivity.
A forced reboot (pull power supply from wall socket) made it resume normal operation.
So the loss of connectivity was a nasty surprise, but once I had noticed the update the fix was easy.
I tried it and it broke again same way. I was trying it around 17:00 CET.
I did read somewhere, that running pkgupdate in shell fixes the issues with updates, but I am not close to router now, so I did not try it yet.