For potatoes, I’ve done it with just high quality potting soil and potting soil mixed with some local mud from the garden.
I am now trying a bunch of potatoes in 50% old mud/potting soil (left over from a large flat container where I grew sweet potatoes - they vine out a LOT - and got about 25-30lbs of harvest from like 4 slips planted) and 50% Gary’s Top Pot potting mix from a local nursery (found this thread with more info on Top Pot - Laguna hills potting mix). I put some compost and fertilizer on the top.
For science, I might try to grow some potatoes JUST in Top Pot with some compost and fertilizer but it’s likely too late for a real side by side test here now.