hola111 PM me if you need help with the modpack
First of all you need to have everything updated meaning that you need the full Custom Maid Ultimate 2020 and update it further with 1.50.1 and the latest dlc.
The issue you describe used to occur on a game version more than 6 months old. The cause is yet unknown and results were inconsistent but it could be fixed if you edited the config.xml with notepad and changed the resolution to 1280x720 windowed and then changed it to whatever you wanted in the game menu. The issue was fixed with a later game update.
The issue can also be related to outdated Visual C redistributables or graphics driver.
Not really related to your particular issue but you can also try to delete system.dat.
EDIT: By the way, back then BepInEx wasn't that popular for COM and Sybaris AIO was still a thing. So it could be that you are still using Sybaris AIO? If so, it's time to switch to COM Modular Installer or BepInEx AIO. I suggest CMI for starters just to confirm that it fixes your issue.