The git branch 5.5 was created, therefore the master branch is open for adding new features, to be part of future Kamailio release series v5.6.x (or whatever version number will be decided during the development phase).
Any bug fix committed to master that applies to 5.5.x or older stable branches should be backported as usual with:
git cherry-pick -x COMMITID
to appropriate branches like 5.5 or 5.4.
Expect that v5.5.0 will be released in a few weeks from now.
Based on the workflow used during the past years, the next future release v5.6.0 should be out after another 6-10 months of development, plus 1-2 months of testing, so sometime by the end of 2021 or in the first part of 2022.
Thanks for flying Kamailio! Stay safe!