There are a million ways of going about it, depending on what fundamentals you want to train. You could try a small "pure" Express/React web site. That basically removes all "magic" except React. Would force you to write a good bit of "vanilla" JS/TS on the backend and some react stuff for front end.
If that feels too simple, one can try a regular NextJS website without the things that would make it "T3".
But honestly you can you just go for it all at once and figure out the parts you don't understand as you need em. It might seem daunting, but everything really can be split into managable pieces