PSX (along with GBA, Atari 2600, and other systems) emulators do not some with the system BIOS, which is essentially the firmware of the physical system. We can’t help you find the actual BIOS for legal reasons (but a google search will provide what you need).

The file name and where to put the BIOS once you’ve acquired it is in the wiki here (https://github.com/RetroPie/RetroPie-Setup/wiki/Playstation-1)

That all being said. I’ve not yet come across a game that has major issues without the BIOS.(I’ve also not played a large number of games for ps1 without BIOS yet either fwiw)