The problem is double.
First, one needs to convert a Rapid rating into a slow one, which varies depending on individuals.
Then, one has to convert chess.com rating to FIDE ratings, which proves complicated.
I used to think, ratings on chess.com were over estimated by about 200 Elo points, but now, when you look at the chess.com ratings of titled players, it doesn't add up.
One thing is sure only, one can hardly hope to get a FIDE rating much netter than the chess.com Rapid ratings they use to have.
I believe that chess.com rapid rating is atleast 400 points higher than FIDE.
Somehow all online calculators using chess.com and lichess ratings and chess rating calculators by solving positions are giving me 1900-2000 rating.
And the fact that I haven't played any OTB tournament in past 4 years but have been studying chess makes me wonder.
If you've never played OTB you have to get used to it first... so maybe below 1800.
But if that happened, it'd go up pretty quickly after you started playing regularly.
Update: I used to OTB tournaments ( Non FIDE rated) 4 years back.
My best score were draw against 2100 FIDE, draw against 1980 FIDE, win against 1800 and few 1700s.
But during that time I also used to draw, lose few games against 1400 and 1500s.
So I am not sure. I have improved my game play since then.