i guess there are some issues with Atomiswave on 5.26 beta for RPi3.
you could help with reporting (feedback is always welcome) in this thread:
Update: i just tested one Atomiswave game (Dolphin Blue) on my RPi3B+ with the current beta of 5.26 and it was working.
But it runs a bit slow. Guess RPi3 is not powerful enough to play Atomiswave games fluently with 100% fullspeed.
foxp4v check if you have the proper bios files and check your roms (maybe try roms from another source)