Start anew at the very beginning: Check the alignment of the derailleur hanger. Set the limit screws according to the manufacturer's guidelines without the chain and cable. Size and fit the chain according to manufacturer's guidelines. Make sure the B adjustment is good according to the manufacturer's guidelines. Ignore perfect indexing at first, but make sure the shifters will move the derailleur all the way from the smallest sprocket to the largest. Then adjust the indexing.
If the indexing is good, but messes up in the middle of the cassette somewhere, it could be the derailleur hanger is not perfectly aligned. So make sure that's good first thing.
Another thing that can make shifting in certain sprockets poor in spite of good shifting elsewhere is a mis-match between a new chain and an old cassette which is worn in to the old chain, or vice versa. Could this be an issue?
Good luck, but these things should help.
Last edited by Camilo; 11-27-22 at 08:50 PM.