OK this is bothering me a lot
since I'm back using gnome, Nextcloud client on ubuntu keeps asking for my godamn authentification each time I start my computer
TLDR: my computer had both kde and gnome, nextcloud was using kde wallet
Installing both KDE and Gnome isn't always a good idea, it can lead to some conflicts and this happened on the nextcloud client
nextcloud was still using KDE wallet instead of gnome keyring to store its passwords, so each time I unlock my session on gnome, nextcloud was lost because couldn't find it's password, since kde wallet was still locked
the bright thing to do would be to remove kde completely, but it can remove useful apps so
I've just opened KDE wallet, opened the wallet and deleted everything related to nextcloud
Now it works
happy me