Ok, so first I am assuming that your mac is not one of new ones with "Apple Silicon" (the new 13" models released in November). If it is one of the new ones, the following does not apply, at least not in the same way.
1) Resetting NVRAM: shutdown your mac; press the power button and immediately press and hold these four keys: Command, Option (in some keyboards it is called "alt"), P and R. Keep holding and let your mac restart some 4 times (it does so automatically), then release the keys and let it start normally.
2) Starting in Safe Mode: shutdown your mac; press the power button and immediately press and hold the SHIFT key. Keep pressing until the Apple logo appears on the screen.
Safe Mode will take longer to start, will clear some stuff and do some testing; it will also only load the essential software.
It is common for problems NOT to occur in Safe Mode; when you have a problem and it does NOT occur in Safe Mode, you will know that it is caused by some third party software that simply is not loaded when you use Safe Mode. This will help us in figuring out what the problem might be.