There should be a "FPVFreerider.exe" file (about 17 MB) which starts the simulator.
There should also be a "FPVFreerider_Data" folder (about 270MB for the latest full version of Freerider classic).
If this is not the case, please try to download the zip file from Itch again.The zip file should be about 117MB.
If it still doesn't work, try unzipping it to another folder, or try a different unzipping software.