ODK Collect v2026.1.0 is now out! It has the full implementation for creating and updating multiple Entities from repeats and groups, including offline. You can create or update as many local Entities in a single submission as your device performance will allow for (most likely limited by expressions in repeats).
We're not officially announcing it yet because XLSForm support is pending, now projected in Central at the end of February or beginning of March, we'll update as we get closer! For the very eager, you can use the repeat column for now, try @Lindsay_Stevens_Au's work in progress at https://github.com/XLSForm/pyxform/pull/818 or modify your own XForms following the spec.
As I wrote above, our current plan is to remove the repeat column on the entities sheet entirely. It was never documented and we're confident only people who follow this thread have used it. If you have an XLSForm with the repeat column, it will fail to convert in the next Central release and you will have to switch it over to the updated format once it's supported. That said, any published form you have based on that column or created by hand will continue working in Collect, Web Forms, etc.
Please let me know if you have any questions.