We were having trouble with the Godot editor taking a really long time to open the project on Windows. During the part where it scans each file in the project, each file took several seconds to clear, making closing and reloading the project take many minutes on some older computers.

Ultimately, the cause turned out to be Windows Defender – this file-by-file scanning behaviour is perhaps considered suspicious by it.

Adding the Godot process to the exceptions list in Windows Defender solved the problem, and now opening projects is zippy once again.