I’ve never tried any of them myself, as I’d just prefer using the website on desktop, but here’s a list of mobile and desktop apps for Lemmy (just look at the right column to see which ones are desktop clients).

It looks like neonmodem is available in the AUR, though it’s a CLI utility. If you’re looking for a GUI, there’s lemoa, but it’s currently unmaintained, or lemonade which appears to be pretty minimal.

Your options are pretty sparse, so you’re probably best off just using a browser if you’re looking for a GUI. I hate to be one of those guys, but you don’t need an app for everything; the browser can sometimes provide the best experience.