dmu

I'm a bit confused, since you said you lived and worked here last year, but are currently in the UK, wishing to join your gf in Lyon. To benefit from the WA, don't you have to be in France and prove continued residence, etc.... before 31st December 2020, when applying for a residency permit on-line? If you're in the UK, you'd need a Visa from the French Consulate before you can return here.
Or have I got it all wrong?
And bear in mind that, even with a Visa in hand, you'll have to contend with the Covid restrictions and its consequences on employment.
Sorry to sound like a Cassandra, but do make 100% sure that your "only option" is viable.
HTH