Hello,
If you install MediaWiki from Debian packages[1], experimental[2] 1.39.0~rc.0 packages are available[3]. These should be usable on Debian 11 (bullseye), Debian 12 (bookworm/testing) and Ubuntu 20.04 Focal and newer.
And a big shoutout to Taavi, who did most of the work in getting updated packages ready as the newest member of the MediaWiki packaging team. :-)
[1] https://www.mediawiki.org/wiki/User:Legoktm/Packages [2] https://wiki.debian.org/DebianExperimental [3] https://ftp.debian.org/debian/pool/main/m/mediawiki/
-- Kunal / Legoktm