Here's generally how it works:
https://youtu.be/sEFP3CsntNs
1. Load in all your files
2. Select Movie Mode / TheMovieDB
3. Click Rename

Looks like the GTK theme is broken on your machine. No idea why that might be.

If you're using FileBot remotely, then I highly recommend using the CLI tools via SSH rather than some kind of remote desktop thing.