There's Vorta: https://github.com/borgbase/vorta which I quite like.

Deffo recommend Vorta, good ui, very reliable

Vorta looks really awesome, maybe awesome enough that I might switch from Back in Time.

I made the switch! Vorta works very well.

Hey, you can't just mix quadrants like that.

If you don't mind a paid app, there's also Baqpaq (written by me) https://teejeetech.com/tag/baqpaq/

Besides vorta (which offers a lot of options) there is also pika backup (which might be simpler by offering less options).

Python source code? Yes, it is on https://github.com/borgbackup/borg (if that was the question).

No cloud? Indeed, borg does not integrate cloud functionality.

You'll either need a directory or a server with ssh and borg to store your backups into. Some people use rclone to clone their borg repos to the cloud.