There’s a fair number of brands selling mg alone and fe alone. Maybe it’s hard outside the US? Or maybe places like target and CVS don’t carry them - those places do have limited options.

CVS’ own brand has Mg only

https://www.cvs.com/shop/cvs-health-magnesium-glycinate-200m...

You can walk into target, Walmart, CVS, etc and have plenty of options for iron alone (which isn't widely packed with other vitamins outside a multi) and magnesium alone.

Yeah, I don't think I've ever seen Mg supplements with other stuff added. I'm currently using glycinate and taurate in powder form, and there's nothing else listed.

I sprained something in my lower back badly enough about a year ago that it took four trips to the chiropractor before I could get out of bed in the morning without lots of swearing. After that, it would seem to be getting better for a few days, then regress into spasms again. After a month or so of that, I remembered that Mg is supposed to be good for tendons and ligaments. I took a good dose of Mg that night, and it was significantly better the next day, and improved from there. That's the only time in my life that I've had a clear, major difference from taking a supplement.

B12 is water soluble and does not cause neuropathy. It was a error by the original poster.

As for methyl vs cyano, it depends whether you have the genetic factors that would benefit or not from methyl groups. In my case I wouldn't benefit so I don't take the methyl form and instead take the hydroxy and adeno forms.

Cyano is useless. Needs multiple steps in the liver to convert.