So, I used to play this game a lot so many years ago and have recently downloaded it again on steam but I want to transfer my progression, is it possible?

As far as im tracking, there is no link.

You would just log in with your normal forum account. There's no use of steam accounts in the game

I figured just as much when I opened the app after posting this but how are my achievements tracked if this is the case?

Dunno, I got all the belt achievments when first logging in but no clue about the rest.

the rest are also tracked im a steam user but ive also been using the steam version since release so take my input with a grain of salt

No I have asked this question before. Linking accounts isn't possible because of how difficult it would be to prove that its "really" your account. Plus qi merging is unheard of. But you can just use the same account you use on the online downloaded version, on steam. everything is connected.

only through steam. Regular achievements got taken down or something

in any case, achievements other than belts were/are seperate

Since everything is server based, you cannot lose any "progression" beside "skill"
All your colors/items should and must still be laying in your inventory

As far as i know, there is no need to link progression since everything is server sided thanks to your account(+ achievements ain't that big of a deal to be honest, beside belts at most.)