I’ve never used it, but:

https://github.com/Vidi0/scratch-io

Says that it’s a Rust-based command-line client, which is probably the sort of thing that I’d use myself, if I were on the hunt for a client, sorta analogous to lgogdownloader for GOG.

Note that it says:

Due to how the itch.io API works, it is not possible to update a game in-place. To update a game, you must remove it and install it again.

Itch has their own launcher that supports Linux. Should be on their download client page.

For actually running the games, I’ve been using Heroic. That doesn’t solve the problem of actually downloading them though.

lutris stilll works.