Just got SS trophy.
Total playtime 82 hours and 300.000 tetrimino spins.
I had some Tetris experience before with Tetris DS, Tetris ultimate and Tetris friends.
I can confirm that you can get SS on endless Marathon, Countdown and Mystery and still get the SS trophy.
Furthermore, I got SS ranks on all normal journey levels except the last one (metamorphosis, S rank) and the trophy still popped after I got my last SS rank on combo.
As for tips on SS on sprint and ultra, the more you play, the faster you eventually can stack the pieces mentally head. This will greatly increase the rate of tetriminos per minute. Another important tip is finesse, finesse helps you put the pieces in the correct spot with the lowest number of inputs.
My first sprint record was around 1:35 on Tetris effect. I practised 2 hours sprint every day and saw my PB dropping by 1-2 seconds almost every day. Just focus on stacking as flat as possible. Try to not stack some pieces vertically for example S or Z pieces in certain situations. Try to use your line clear animation as a small pause to see your next moves.
For Ultra, I used back to back Tetrisis. I try to combo my back to back Tetrisis for extra points and try to get 32 lines around the 2 minute mark and 64 lines at the 1 minute mark.
You will need around 96-98 lines clear to get 35K points without breaking your back to back bonus.
I wish everyone attempting this trophy all the luck.