So I was doing the civil wars quest on my new character because I want the windhelm house (im an imperial) and then after completing a couple of quests I remembered reading something about if I complete the civil wars before the main I won't be able to complete the main quest, now I read this a couple months ago and couldn't find anything on google that says if it's fixed, so my question is if I finish the civil wars quest on the imperial side will I be able to do the main quest ? Thanks

That is incorrect. You can safely complete the civil war quest without fully completing the main quest.

Yes, yesterday I finished the main quest after I already completed the civil war quest, and I took the imperials side.

Wonderful, thanks !