As a solo, in other extraction shooters like EFT, I do a lot of sneaking around. Trying not to engage as I don't want the attention. Maybe one shot here or there to kill a scav or even a player if everything lines up perfectly. In Active Matter, I cannot do that. I get that you don't want people camping, so spawning invis and hell hounds and makes sense to keep people moving.
Maybe if there was a "repellent" that a solo-only could wear, that changed the range before mobs would aggro to you or something like that, so you could sneak around more. That might help solo's.
Alternatively, a solo-only queue would likely also help a lot.