In looking at this further, form 5329 doesn't appear to be correct. line 18 (enter your excess contributions from line 24 of your 2020 for 5329. If zero go to line 23) is incorrect. Line 18 has $6000 (which is the amount of my 2021 excess contributions. I had no excess contributions in 2020). Excess contributions for 2021 is blank (line 23). Total excess contributions, adding lines 22 and 23 is $6000. it looks like the penalty is for 2020 and not for 2021 - I had no excess contributions for 2020. Not sure how the years became mixed up.
