When opening a large project (such as Marlin) the IDE tries to load every single file inside the project folder, but after a certain number the opening of each file takes a couple of seconds.

Steps to reproduce the behavior:

1. Open Arduino Pro IDE
2. Open a large project
3. Wait

In my opinion when opening a project just the .ino file should be opened, or at most the files in the root of the projects, and not in subfolders. This way only essential files are immediately opened, and other files can be seen in the Explorer.

I doubt anyone would be using Classic mode for large projects, the drop down menu gets annoying to use with a lot of files.

Device:

• OS: Windows 10 2004, build 19041.572
• Version: Nightly 20201022