Also, posts like yours show up in /r/nootropics every day. "Taking supplement X changed my life!" Almost always sound like placebo, especially when it's a medication that takes weeks to have an effect and the user claims it fixed their life in a day.
Trying to fix Potassiun alone wont work because Magnesium is required to absorb it, or something like that; can't remember the full details now.
And obviously if your symptoms are actually from a Potassium deficiency, trying to fix Magnesium alone won't work either, if you're still not getting enough Potassium.
So, your best bet is magnesium supplements and lots of bananas :p
I don't disagree with the rest but talking from my own personal experience, taking magnesium had almost an immediate effect on me but perhaps it's not the same for everyone.
Totally agree that there are other factors that may contribute to muscle soreness but I think taking magnesium is a good, harmless experiment if you have not tried. Also perhaps you may find other potential answers reading through some of the responses here :) Good luck mate!
Sure the people that claim it fixed their problem in a day, it's probably a placebo, but I suspect for some people things really do help them.
If you eat a "balanced diet" (whatever that means), then you probably don't need any supplements. I noticed after I was drinking Huel for breakfast for a few months, I felt much better in general.
Sadly, this phase is also when most people write their reviews of supplements.