What is Serius Sam Classics: Revolution? Is it a new game or you can just play first and second encounter in one place?

Can someone help me with the Roadrunner achievement please ?

I just beat my high score in Neon BUT it is stuck on old score.

Whenever I try to launch it, I get an error message that says "Permission denied," even though I've been playing the game for about 2.5 hours this past week

It's a pity that the Croteam developers refused to develop Serious Sam: The Third Encounter, if the plot and scenario are known, then why don't the modders develop it ? I saw a video of Serious Sam: The Third Encounter on the Serious Engine 3, and I want to know, is the development coming from the modders ? Or is it silence already ?...