Same problem as STRIGIDI.
Have contacted support about this back in september 2020 but no solution from Arturia other than clean registry for all midi entries and reinstall MMC.
Did not solve anything.
Have installed MMC on two different PCs now.
On my 11 years old desktop pc MMC works fine. Running Windows 10, version 1909, build 18363,1139.
On my 3 years old laptop pc MMC won't start. Runing Windows 10, version 2004, build 19041, 572.
If this is the reason why MMC works I don't know.
Please Arturia, look in to this and update the MCC sofware if this is the case.