Hi shmerl!
Try adding this in ~/.config/Epic/HeliumRain/Saved/Config/LinuxNoEditor/Engine.ini.
[/Script/Engine.Engine]
SmoothedFrameRateRange=(LowerBound=(Type=Inclusive,Value=40.000000),UpperBound=(Type=Exclusive,Value=999.000000))
This should effectively disable framerate smoothing, and ensure you can get higher framerate.