Project indefinitely loads when opened

Editor crashes can happen for a number of reasons. A short-term solution is that you can hold the "alt" key while opening Unity (that is, immediately after you click or double-click to launch the Unity editor, hold the "alt" key), to bring up the project selection screen. From there, you can work on other projects.

To attempt to solve the editor crash, create a folder in a separate location where you can move files and directories you've moved or created within the project folder since the last time Unity ran successfully. Add files back to the project's directory (add empty directories first, and then add the corresponding files) one at a time until you find the offender. At that point, more specific guidance can be given on why that action causes the editor to crash.