So 10 X F1 2020 cars TP need 60*10=600 tunes to fully upgrade all of them.
Looks like each of the 9 GP will only allow 28 upgrades each so not enough to fully upgrade more than 4 x TP.
The only other way of earning TP seems to be to install and swap tunes between cars of the same ilk. Installing a tune pays 25 TP XP so needs 6 x installs to collect 150 TPXP.
No idea how much more convoluted this can get but need to bear this in mind whilst choosing cars to use for the GP as once you max your TP or all that TPXP goodness will go to waste so might be better to choose a different car for the first four or five GP.
The lack of information about how all this really works is shocking, despite the multi-page innane FAQ, and players are left to deal with the aftermath and find out for themselves,