LRC is not starting

Did you click 'Doorgaan' to see if it starts up nevertheless? The message says that you could get a problem, not that Lightroom Classic won't work. If you do get a problem and another error message, then post it here. But check this first: Go to MacOS 'System Settings - Security & Privacy' and add Lightroom Classic to "Full Disk Access" if it is not in there yet or not enabled. See Quick Tips: How to give Full Disk Access to Lightroom Classic on macOS

Did you try what the message suggested: click on "Herstellen om door te gaan"?

What happens if you restart the computer?