Unfortunately, we discovered an issue with Cinema 4D R19/R20 on the latest Windows 10 Builds (20H2 and onwards).
After installation of Cinema 4D it won't start or disappear immediately.
If you discover this issue, you should create a new rule in the Windows Firewall (or other firewall used), that blocks outgoing connections for Cinema 4D R19/R20.
This should solve the issue and Cinema 4D will start correctly.
The disadvantage is, that the online updater can no longer be used for automatic updates.
You can find a tutorial on how to create rules for the Windows 10 Firewall here: