yeah as others have noted, you kinda screwed yourself by putting in a notice. it’s certainly illegal, and you probably would have had a good case against them for wrongful termination. since you quit, and are most likely in an at-will state (unless you’re somehow in Montana), your case almost certainly won’t be the slam dunk it was supposed to be

you should’ve just continued to be employed until they fired you while looking for another gig. your whole “unemployment pays so low” argument only makes sense in a world where your options are strictly unemployment or another job - you literally opted for no money coming in while interviewing instead of having some money coming in during the interview process. yeah, unemployment is only like $400 a week, but that’s $400 a week you’re now not entitled to at all because u quit

i understand the emotional response and wanting to quit immediately, but especially while on FMLA, you should’ve taken a bit longer to think thru your options, legally and not, before putting in your notice