Mind maps you could do on paper and scan in. You don't need such good handwriting for them. But I can see how you may still want software for it.. you may need specialist software for it. I don't know which are good. Google shows that tony buzan has an expensive one. General note taking software may not be as good or good enough if it has such a feature.
For notes I find Ms Word or notepad ok, and make sure you have autosuggest on so you can get around the directory tree better to safe files. You could use pasteitin to paste in some long paths at the touch of a button.
For typing maths in. MS Word has an equation editor.. I used it about 10 years ago. Insert..Object...Microsoft Equation..
It's good for basic graphics too. Not a huge mind map..
Do turn off the annoying drawing canvas thing though tools..options..general..deselect "automatically create drawing canvas when creating autoshapes"
But consider, you may not need more than an A4 page for a mind map 'if you want the thing to fit on the screen so it might go in your memory better.. So, MS Word may be fine for that too. You can draw circles lines and textboxes.