Thanks for the update. I guess I don't understand why, if there's no development happening on the v3 branch, the code would have changed enough to make the patch invalid! I'll have to look into it myself.
We do want to upgrade to v4 when possible, but the issues that arose from updating to CKE 5 were so time-consuming that the client in question just wants to get existing footnotes fixed first before assessing the time required for an upgrade. Not a lot of hours available to put into the work. I'm sure the upgrade path you pointed out has taken a lot of possible formats into consideration, but there are thousands of entities using footnotes on the site and it's hard to trust that we won't end up writing custom queries and upgrade hooks to fix the edge cases.
I'd like to make use of this, but the patch from #10 doesn't seem to apply anymore to the latest revision of 3.1.x-dev. Is it straightforward to reroll?
If, heaven forbid, you are like me and need to upgrade to D10 while still using this module, here is a patch that will stop composer from yelling at you.
brendanthinkshout → created an issue.
This patch seems good to go on its own merits, but trying to test it with the example migration setup has exposed some deep weird issues with the core migrate module and how it handles data coming from Google. Will write up a blocker issue.
Here is a patch to empty out the function if you don't have the capacity to upgrade and then downgrade again.