For 2 days I have no longer been able to create access to my Nextcloud for the Nextcloud client. No matter what OS (Arch or Debian), no matter what browser I use (Firefox, Falkon, Vivaldi). After entering the credentials and being asked “Do you want to grant access?” I stay in a loop that keeps expecting the credentials.
Since I haven’t had any problems for 3 years, I’m a little surprised.
For Linux is Nextcloud-3.17.3 as Appimage available
I had already tested 3.17.3 as a flat pack. The error is the same here too. After I am asked for the credentials a second time, the message “Access prohibited, status token is missing.”
This message already appeared in 2022 under this link and apparently only solved for /e/murena and not for the desktop.
I’ve had the problem on the desktop since October.
I am a big fan of using no snaps, no Flatpacks and no AppImages. My nextcloud client is out of Ubuntus deb-Package. It works.
It’s difficult to say, as you omitted the support template and we are therefore missing various details 
. But here’s a wild guess:
you’re using Cloudflare or another reverse proxy in front of it, right? Such problems are often encountered in combination with incorrectly configured reverse proxies.
Im having the exact same problem. I use a reverse proxy to access my NC but it has never given me this kind of problem, it started ocurrig all of a sudden. Also seen @mritzmann response but if this was the case, wouldnt it also affect normal logins? For me this problem is only related to logging in on NC mobile app and specifically when granting access.