Persona 5 Royal
I want to get into SMT, where do I start?
with a life stone.
Worst possible option to start. Most people that start with a Persona game won't get out of that bubble ever.
It's better to start the series with a mainline Megaten game, that way you can get to like almost all of the series in the franchise, including Persona.
SMT IV, DDS or Persona 2
Don't start with nu-persona, they're great games but you'll have a hard time getting into mainline SMT after that
Nocture is likely to kick your ass and make you drop it, the other options are more newb friendly
SMT4 to pick up the mechanics quickly.
Then you play whatever else like SMT3, DDS1/2, and Strange Journey
You can easily branch out from 3 or 4, it's usually P5babbies the ones that don't bother with previous games in its own series or even acknowledge any other Megaten game.
SMT IV or DDS. play noct after you finish one of those
Persona 5 The Royal
I started with Devil Survivor and enjoyed it more than IV. I think it's still fucked on Citra although apparently an older version can run it fine.
I started with Persona 4 vanilla and P3P after that and I managed to transition into real megaten after that with DeSu, Strange Journey and then Nocturne. I can see where you're coming from but I don't think it's always the case.
Anyway OP I recommend Nocturne, Strange Journey or SMTIV.