I recently started using libsrtp2-dev (on RPi) and the last I checked, nothing complained on either Stretch or Buster. I don’t do any SRTP, however, so I’m assuming it’s working.
ucp v14.0.3.6 and ucp v15.0.6.6 (both EDGE modules) now use pkg-config instead of libicu-dev to determine the underlying OS, allowing UCP to install and run on both Stretch and Buster.