if you ask me, and if given the condition that i only can do ONE exercise in my whole life, it would be barbell back squats, the king of all exercises.

If two, then add in barbell bench press, just the basic flat bench, no fancy mancy incline la decline la close grip la bla bla

If three, then most definitely the conventional deadlift.

If four, throw in pull-up, and slowly graduate to weighted pullups.

If five, running, but nothing more then 5km.

Fitness is a lifestyle, not a seasonal hobby, so keep it simple, basic, easily repeatable. Stop believing those tiktok/youtube exercises which is obviously created for views only, thats their job - to get more views.