We need a version of the [transactions SPI|transactions SPI_] which is compatible with Jakarta EE 9.
The plan that other projects are taking is to have a second set of artifacts using a different GAV released in parallel with the main releases by using build time transformation.

Note that at least Hibernate ORM require a compatible Transaction Manager: they use Narayana to run their integration tests, but they also promote its use to end users by having it included as default dependency of secondary artifacts they release to help people writing their own integration tests, reproducers, quickstarts, etc..