Windows 10 desktop client can't log in

Hi there! I had a working Nextcloud server running with well-functioning iOS and desktop clients. I had to reinstall the server + new wildcard SSL certificates (Let’sEncrypt). Now I can use my iOS app and the web to log in but the desktop client can not log in, I get the “Failed to log in at … Unknown error”. I have tried to reinstall the client without any effect.
Server version: 17.0
Client version: 2.6 stable
Log file: not present as I can not log in

Any ideas?