TrainerRoad is a great app with some very good people behind the scenes.
I used TR and other similar apps for a number of years and made some decent gains. The workouts and plans will definitely get you fitter.
I now do about 95% of my riding on Zwift and I actually ended up increasing my FTP more purely because I found it so much fun to use and actually really looked forward to getting on the turbo for the first time ever.
I loosely stuck to an 80/20 plan and it worked.
Everyone is different and I do think a mix of the two platforms can give you great results.
Since Zwift I’ve struggled to put myself through the pain that TR can dish out and just seem to be able to push more during group rides or races on Zwift.
I’d definitely say for you to give TR a try though because if you can commit to doing the workouts you will get fitter.