[2019] Game downgrading to an older version of the launcher

This is very odd. Has he tried to ‘Verify Integrity of Game Files’ instead of reistalling?: https://support.fatshark.se/hc/en-us/articles/360021233534--PC-How-to-Verify-Integrity-of-Game-Files-via-Steam

Additionally, which Anti-Virus/Firewall is he using?