If you have a Wacom-style graphic tablet and you need a simple and distraction-free painting program, MyPaint seems like it could be a really good fit.
Now that the huge update to Slay the Spire is live adding in The Watcher as the fourth character, Mega Crit Games have also updated their opt-in game engine upgrade Beta.
A rolling-ball physics platformer where you move like slime, jump like a bouncy ball and swing using a sticky tongue like a weird version of Spider Man. Crumble has a lot of fun ideas going for it and a big demo update is out now with co-op.
Gamesbymo have announced that A.N.N.E, the crowdfunded mixture of metroidvania style platforming with space shooter elements will get a big 1.0 update on May 20.
The team behind RetroArch, the open source and cross platform frontend/framework for emulators (and a lot more like open source game engines), have stated their plans for handling the various emulators it works with for the Steam release.
Former Google developer Adrian Marple quit to become an indie developer, with the puzzle game Obversion being their first title which is releasing next week.
A genre Linux surprisingly doesn't have a huge selection in is Match 3 puzzle games, thankfully if you love these casual games a new one is out with Tower Of God: One Wish.
Godot Engine, the quickly improving free and open source game engine is getting real close to a major release with the first Release Candidate now up for Godot 3.2.
Boxtron is another awesome Steam Play tool! Covered here a few times now, like Proton it enables you to play games on Linux that don't have a Linux build setup on Steam only this is for DOSBox games.
I grew up playing the early Sonic games so Open Surge really speaks to me. A retro Sonic-inspired platformer (that's actually quite polished already) and a game engine for others to create with it.