As others have said, you are spending money on a bike that is not high quality. There is a difference between an older quality 26” mtb and cheap 26” mtb.
If you are upgrading just for the sake of it. Don’t waste your time on a new fork. A co-op is a good idea. Unfortunately cheap higher quality vintage forks in excellent condition are no longer throw aways. And maintenance is an issue.
Keep riding your Huffy and keep your eye out for a good 10 year old, or so, 29er. Mtb’s have changed so much in recent times that older, but not yet “vintage” bikes are not in as much demand, pandemic issues aside.
Most stuff goes from a cheap people no longer wanting it to a highly nostalgic expensive collectible, you just need to get one when it has fallen out of favor.
John