Fun fact, you can also automate more of that existing workflow with the rebase interactive TODO list. Roughly something like:

    pick $ACOMMIT1
    edit $ABMIXEDCOMMIT # split out A parts
    pick $ACOMMIT2
    exec make test # test everything compiles
    update-ref bugfix/A
    exec git switch --detach main # new branch point
    pick $BCOMMIT1
    edit $ABMIXEDCOMMIT # split out B parts
    pick $BCOMMIT2
    exec make test
    update-ref bugfix/B
    exec git merge bugfix/A
    pick $FOLLOWUPCOMMIT
    exec make test
    update-ref intermingled-branch # or bugfix/C

It's been a while since I've attempted a rebase TODO list that wild, so I may have forgotten something, but rebase interactive is pretty wild what it will let you try to automate.