I own almost all routes in TSW2, but Mastery only offers me Sandpatch, Bakerloo and Cologne-Aachen. Shouldn't that be a few more? Or do they not exist yet? Another problem: the game sometimes seems to randomly log out of Dovetail live in the background, then achievements are not added to Mastery.
Hopefully some more of the routes are added to mastery in the future btw you will probably get more responses if you put this in the pc/Xbox / PlayStation disscussion areas of the forum
If you have preserved collection routes you have to do the mastery in TSW2020 to unlock those rewards (carries across to TSW2 I think).
Mastery is linked to your Dovetail Live account, so as long as you are using the same account in TSW 2 as you did in TSW 2020, the scenery tiles you unlocked in TSW 2020 will be available in TSW 2, although you do have to enable them through the Configure Overlays menu option. Unfortunately, the dioramas are not available in TSW 2.