OK, so AIUI remaining work here on this task:
- Backport 704745 and 1220366 to REL1_44, REL1_43 (REL1_45 already done in [original patch and [https://gerrit.wikimedia.org/r/c/mediawiki/services/parsoid/+/1224160|1224160]] respectively).
- For each version of MW,
- Make a release of Parsoid with the above patch
- Pull the new release into MW core and MW vendor
- Apply the patch for T413573 for core
- Apply the corresponding patch(es) for extensions/skins, once they exist, that are in the tarball.
- When the next Quarterly release of MW happens, announce PHP 8.4 being supported, and (only then) adjust the on-wiki claims about PHP 8.4 support.