tests-passed is the default and it’s probably unlikely you switched to main. tests-passed is only behind main for as long as it takes for the automated tests to run, assuming they pass, which I think was about 14 minutes the last time I looked.
In any practical sense, tests-passed gets updated at the same time as main, except where a commit fails one or more tests, in which case a subsequent commit to fix that usually comes pretty quickly afterwards. (Then the tests run, probably pass and it ends up on tests-passed)
As for the version number, essentially stable is explicitly 2.8.8, beta is explicitly 2.9.0.Beta9, tests-passed (and main) equates to 2.9.0.Beta9 + whatever commits have happened since. It will probably change when they have a collection of "whatever commits have happened since" to call Beta10, at which point beta and tests-passed could be briefly equal.