As safe mode seems to work better it might be some software.

Whether its a general macOS issue or the specific version installed

If possible, try to start from another Mac startup disk and check.

Your Mac might be able to identify the issue by that.

Reset NVRAM/PRAM and do a Hardware Test.

If you can measure the MacBooks temperature try to check if its an overheating issue.

You could also try to take out the HDD and connect it to another Computer if this step fails.

Try to save the files with target disk mode and/or recovery mode (I would do both a copy of the raw data with target disk mode and a time machine backup).

This issue may worsen and being unable to access/lose important data is the worst thing that can happen.

Hopefully this little discovery might be able to help others in a similar situation (video hardware crash on startup).The first thing you want to do is to backup your data. If it's between a completely non-functional machine, and one that can't sleep, I'll take the latter. By removing the NVDAResman.kext file from the extensions folder, my machine is now miraculously able to start up in normal mode with no noticeable side effects except for an inability for the machine to be put to sleep.

First I discovered the importance of the NVDANV30Hal.kext file (removing it stopped the start up process entirely for normal and safe mode). I did this one at a time, to see if I could find out what might be causing the problem. Well, after a bit of nosing around on the internet and in a few other forums, I can across the keen idea of going into Single User Mode and removing video-related kext files from the systems/library/extensions folder (very dangerous stuff, I know), sort of like what I was trying to do with the booting the audio kexts to get sound running in safemode (as discussed earlier in this forum). I was able to get things started in Safe Mode, which worked well for the next few months, but a few weeks ago, Safe Mode crashed as well, and everything I tried (with the exception of Single User Mode) resulted in a grey screen with horizontal lines across it (seemingly an indication of a hardware problem). As a final (hopefully) update, the problems I was having with my G4 failing to start-up normally began to recur about two months after I had it serviced at a Mac retailer in Bangkok.

How to turn on macbook pro in safe mode