@Bernhard_Vogler Here are 2 things you might consider doing.
1 To see if Defender is the culprit, add folders to its exclusion list. After each Windows update, settings are usually reverted back to their default, or something that is beneficial to the company, like uploading samples even if disabled previously. Sometimes, it gets new features that you might want to configure.
2 Restart after you uninstall and then restart again after manually deleting the remaining files or registry entries. For some reason, at least on my system, certain files tend to stick around until I restart Windows. Reinstall dt once you are done and everything is truly gone.