My MacBook is stuck on loading screen

Hold Power button in until it powers off then...

Start with this of M1 Mac...

Start up a Mac with Apple silicon in safe mode

On your Mac, choose Apple menu  > Shut Down.

After your Mac shuts down, wait 10 seconds.

Press and hold the power button on your Mac until the startup options window appears showing available startup disks and Options.

Select a startup disk.

Press and hold the Shift key, click Continue in Safe Mode, then release the Shift key.

To leave safe mode, restart your Mac normally, without pressing and holding any keys during startup.

Start with this if IntelMac...

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes or more.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

Follow the advise from previous posting.

Has the Computer issued a warning about " this computer is running low on empty Space "?

If yes, that maybe the root cause of getting " stuck on loading screen."

If lack of Empty Space is the issue - this must be addressed immediately or the computer may stop booting at all.

What is “Other” storage on a Mac, and how can I clean it out?

Free up storage space on your Mac

OmniDiskSweeper Safe to use

GrandPerspective 

How to delete Time Machine snapshots on your Mac

See used and available storage space on your Mac

Locate backups of your iPhone, iPad, and iPod touch

The final word from Apple on Managing the " Other " Category

Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.