I'm planning to upload python3-defaults later tonight, adding 3.10 as a supported Python version. Packages are able to migrate on their own, there are no blockages introduced on other transitions.
We have most packages ready to build for 3.10, and around 70 leaf packages still needing some work. Otoh, we can much better work on these if reverse dependencies are already built for 3.10 in the archive. The tracker used is https://release.debian.org/transitions/html/python3.10-add.html As some kind of reference, the current state of the 3.10 addition in Ubuntu can be seen at https://people.canonical.com/~ubuntu-archive/transitions/html/python3.10-add.html Matthias