HITMAN from IO Interactive and the Linux port from Feral Interactive is a great game worth your time and monies, plus you can try the whole game across this weekend for free.
Basingstoke released back in 2018 and in my opinion, it was a damn fun game that really got my blood flowing. Sadly, it went quite under the radar and it seems it pretty much ruined Puppygames.
Iterative Games say they've combined elements inspired by Contra and Metal Gear Solid to create a cyberpunk side-scroller shooter with stealth elements with Contract Work.
Kalypso Media and developers Yippee! Entertainment have announced that the Commandos 2 - HD Remaster, which will support Linux, is now going to be releasing in 2020.
OFF GRID from developer Semaeopus is a very promising game about sneaking around and hacking everything. After a successful Kickstarter campaign in November last year it's progressing nicely.
Orangepixel have announced that Gunslugs:Rogue Tactics, their action platformer with stealth elements is closing in on a release date and it's looking great.
According to the information on it, Hegemone Pass is a stealth RPG (they say JRPG, but they're actually French). It's set in the Greek Underworld, with combat and exploration mixed in with an alert system
SKYHILL: Black Mist from Mandragora and Klabater looks like a promising survival-action game with some stealth elements and the good news is a Linux version is planned.
Hidden Asset is a game I've been following since 2011 back when it was called Hostile Takeover, it's a real-time stealth game that's very promising and it's now needing funding.
Puppygames, a developer who has supported Linux for many years are now making their games free for Linux gamers and they've already started with Basingstoke.
IO Interactive are continuing to improve HITMAN 2 and to let people have a little taste, the first mission is now entirely free. Thanks to Steam Play, it works well on Linux.
AT SUNDOWN: Shots in the Dark from developer Mild Beast Games and publisher Versus Evil puts an interesting spin on the top-down shooter genre where light is your enemy.