I saw an ad for Mathematics Educators SE in the right sidebar while browsing the main site here. Since the stats in the ad seemed to be out of date, I checked by clicking on "comment" under the ad that in fact it is from the 2020 Community Promotion Ads cycle, specifically it is the one proposed by User Pedro.
I believe this is a bug, since we should be served ads from the 2021 cycle. There is in fact a new ad proposed for Mathematics Educators SE (with updated stats), and it is supposed to be among the ads that are live according to the criteria mentioned in the Meta SE announcement. (I also verified that this ad appears in the list generated by running the SEDE query posted in the same Meta SE post.)
I also clicked on the "stats" link under the ad that I was shown, and it sent me to the Community Promotion Ads Statistics page. All the ads shown there are again from the 2020 cycle.
It would be great if this bug could be fixed and we could have the latest ads up and running!
Update: I just received another ad in the right sidebar from the 2020 cycle, which was for CoCalc, specifically the one suggested by User Viktor Vaughn. Clicking on "comment" under the ad does not send me to the 2021 proposal for the same ad, but it makes me wonder: perhaps this issue is only with ads that have been repeated? I will keep an eye out for other ads and update this post with further info.
Update 2: Now I have seen an ad posted for Operations Research SE, which is the old one proposed by User TheSimpliFire. The new proposal for the same ad is not among the list of ads chosen to go live, as per the criteria mentioned in the Meta SE post mentioned previously.