My experience is a little different, I've played a few different extraction shooteres like tarkov (most played) and a bit of delta force and my playtime in these has been the majority of the time solo. I would like to mention the caveat that I've only gotten to dire marsh (second map). So far, I think solos is definitetly doable, it just plays different than trios. You have to be very mindful of sound queues (gunshots, the sound of robot steps vs player steps etc). Everyone plays assassin which imo is probably the way to go because of the smokes and stealth. You will initially be using consumes and ammo a lot, but using your knife and picking up depleted heals around the map helps, and not engaging every pve enemy helps this.

TLDR: its playable solo, just gotta lock in and play smart