I noticed X (formerly Twitter) app notifications are still shown using the old Twitter bird icon. Whatever you may feel about this rebranding, I think the current X logo should be used. Why hasn’t this been updated yet?

19.18 and indeed it still hasn't been fixed. I know you have to deal with priorities and this might not be very high on the list. But I assume the Twitter logo is just an asset your source code. Globally replacing all Twitter logo assets with the new X logo shouldn't be that hard, IMHO.