@ocelot07
As Hotpots said, you only need to pay to get in the Early Access that is meant to last about 6-12 months. Grinding Gear Games (GGG) aims to release the full game at the end of next year and that will be the official free to play release.
The characters you play during EA will be available in a “legacy mode” to be played forever, but everyone will need to make new characters then the game releases “official” next year (or early 2026 in worst case scenario).
But MTX you buy in PoE2 will be available both in legacy and official release versions of PoE2.
Edit: To clarify even further: Early Access is just a fancy name for “Beta”. The game is finished about 90% right now but need to be polished and finetuned during the EA and act 4-5 and 6 more classes will be released during the EA every other month. The 6th and last act of the story comes with the official release according to GGG. *
* Everything above is subject to change,