Hey,
That screen is Nextcloud’s normal OAuth / device-flow login page.
It appears whenever a desktop client (in this case the one identifying itself as “worker2 (Desktop Client – Linux)”) asks the server for a new access token.
- “Anmelden” = enter your username / password (or an app-password).
- “Zugriff gewähren” = grant the client permission to access your files.
- The yellow box is just a security reminder: if you didn’t start the client, don’t grant access.
Because your token isn’t being saved (nothing lands in KWallet), the client has to repeat this step every reboot. Once KWallet stores the token correctly you’ll stop seeing this page.
Side note: I don’t speak German myself, so I’m reading that dialog through an online translator—apologies if I miss any nuance.
I have not a link for Appimage that you requested.
Did you try Flatpak as I mentioned above?