last year's tax form, proof that I paid rent for the last 3 months, or that I got paid the last 3 months. I just moved here, I can't.
I'm finding it hard to understand how you don't have (or can't get) this paperwork?
Sure, you won't have
French versions of it, but surely you have (or can get) payslips/tax-payment statements from your previous (Dutch) employer, and receipts from your (Dutch) landlord, and/or bank statements showing regular payments into/out of your (Dutch? German?) bank-accounts, from either of the above?
Earlier this year, to prove that I
was in full-time eduction during that previously undocumented 4-year period, I sent off a stack of copies of my (British) A-Level certificates and college transcripts (now 25 years out of date!) to the Deutsche Rentenversicherung. I didn't even have them translated, but I've heard nothing back from the DR since the deadline they set (despite Brexit, which
finally happened in the meantime), so it would appear that those docs were sufficient...
Don't recall reading anything recently about Nexit or Frexit

so presumably the Netherlands and France are still both EU nations, and thus paperwork acquired in one
should be recognised/ accepted/ valid in the other...?
Additionally they,sometimes require that someone else vouches for you. Needs to be someone with a French tax ID, currently living and working in France. I obviously dont know anyone, bc I just moved here, and my only French friend is currently living in Switzerland.
Again, why is this a problem? Isn't your new employer(s) French and living in France?
I mean, they invited you to work for them, so presumably they have confidence in your ability to do the job they hired you for (and also in their ability to pay you for it!), so why can't
they vouch for you?
Does a 'voucher' put themselves at risk of incurring some kind of fiscal/legal liability if the 'vouchee' turns out to be a flake?