My guess is 23:

Yuuki Yuuna S3 will be debuting in a couple days, bringing the great anime that has aired this year count to 21.

If a BanG Dream movie gets released before January that would get us to 22.  Girls und Panzer is slated for release in late December, so that would get us to 23.  Alternatively maybe the Kiniro Mosaic movie will come out in time, or some other surprise.  But however I add things up it looks like there will be 23 great franchises airing this year.

This would be less than any year going all the way back to 2006.  But of course 2006 featured Higurashi, Code Geass, Haruhi Suzumiya, Utawarerumono and Kanon, so it didn't need many series to be great.  If you look at quality and quantity combined 2021 is worse than any year going back to 2005.  It's weird how bad anime has gotten over the last two years when there are so many good series announced to be in the works.  The problem is announced does not equal aired.  The past of anime was bright, the future of anime is bright, but the present of anime sucks.

There are 30 great anime franchises with announced sequels in the works.  There's no lack of good content.  The problem is purely scheduling.  Stuff that's been announced for years still haven't happened.  I can only assume Covid-19 lockdowns are affecting the production speeds of all these various series.

If everything that's been announced came out next year we'd be back to the healthy old days of 40 franchises a year.  I guess that's a little overambitious, but still, we could do a lot better than 23.  And it wouldn't be minor series either, or all singular ova's/movies.  We're talking Fairy Tail, Bleach, Love Live!, Idolm@ster, Utawarerumono. . .*sigh*

Combined with the previously unheard of dearth of visual novels  it's really been a tough year.  The same as anime, there are plenty of great visual novels announced as being in the throes of translation.  Rewrite, Summer Pockets, Kud Wafter -- recently Sen no Hatou was announced.  But perhaps due to Covid-19 as well, but for whatever reason, nothing has actually come to fruition.

On the bright side, that could mean 2022 is going to be an absolute bonanza.  Or maybe everything will be delayed to 2023. . .