I hear you. The mix of managing agencies doesn’t make it any easier, either. San Jacinto is especially weird, b/c it’s state park in most of the areas with sanctioned backcountry camping. All of the trails are open on San Jacinto, but yeah, no backpacking. They did determine that it’s okay for people to be together on the tram, which reopened recently, so it seems odd that they’d think backcountry camping isn’t at least as safe as that, right? Alas.
It’s cool enough out this time of year to camp in the Santa Rosas, south of San Jacinto, and some of the lower elevation stuff that’s too hot until fall. Might look into that. Another possibility to consider is heading up the Whitewater. There’s probably restrictions on camping along the PCT, but heading up the whitewater and into it’s tributaries makes for adventurous cross-country travel, and after a mile or so beyond the trout ponds becomes very wild and remote. you could start in from Mission Creek, or park along the road below whitewater preserve (the preserve itself is closed). Another consideration would be the Orocopias, south of Joshua Tree.
There are creative, non-traditional backpacking options. Just have to dig around a bit and maybe drive a little further.