Thanks to Jimbatron for the epic neat boat jump:    • GTA Online: Cayo Perico Heist  Solo ...  
and byeolchanara for the epic solo gold method:    • 그타 문열기  

mostly works with these 2 specific doors in the vid at west and south storage according to sources and some of my own sloppy testings.
apparently also possible to pull it off with the north storage thanks to this video:
   • [GTA] [Patched] Cayo Perico  Open wa...  

press Q to take cover against the doors (ideally closer the better), then A to position the character facing towards left.
press and hold D then Mouse Right Click right when the character makes the turns, adjust and find the optimal character positionings and camera angles.
(for the keyboards obviously, have no idea how the controllers works;)

basically just 'somehow trick the game into thinking you are opening the doors from the inside but actually not' or something like that
recommend to slightly adjust various character and camera positioning if stuck without progress for too long, or just drop it, 'get a friend' to open the doors legitimately and stick with coke solo since the glitch can be really frustrating in the end.
or eventually open the doors first try after getting really familiar with it.

cash from the safe can prolly go 10k more higher but didn't bother with much grindings cuz that south storage door first try tho; 01:45
might take quite some times of fail attempts to get the positioning or control timings correct as struggles shown at 02:15

some basic experiments here:
   • Collect goldz solo, nonaggressive ve...  
   • Sneaky Solo Gold Testss 10:54