Not just Imola and Portimao on Project Cars, they also have Mugello, Nurburgring and Bahrain Outer. Only Istanbul not available from the missing 2020 tracks.
I would hope that for F1 2021, some sort of provision is made to have the correct circuits. They have the Project Cars data as mentioned above, plus they will have some data from the races last year at these circuits (lap timings, racing lines, tyre wear etc) so it all helps.
I would guess F1 2021 is well in progress and if they can't include the alternate tracks in the game at launch, they do look to add them in a DLC (either free or paid) at a later point. Then as mentioned above, give the user an option to amend the season schedule to add/remove different circuits. The only issue i guess could be licensing plus you would need to get Crofty to record some more intro's for all the different circuits.