You can switch liquidsoap to an OPAM install of liquidsoap 1.3.* as described in the liquidsoap docs or install the testing (aka Buster) packages @paddatrapper pushed (along with the libfdkaac-ocaml-dynlink and fdk-aac packages from testing non-free).
You might also need to patch your LibreTime installation according to the instructions in LibreTime/libretime#192.
That should get you both AAC and HE-AAC (AAC+) since lots of fixing was recently done. Currently %fdkaac which supports both AAC standards only works for Icecast, SHOUTcast support should be working in 3.0.0-alpha.7. The old %aac and %aacplus encoders in liquidsoap are obsolete nowadays (in current liquidsoap 1.3.*).
Given the “official” statement on gnu.org it doesn’t look like fdk-aac will have a rosy feature due to its GNU incompatibility. It’s to note that it depends on how you compile fdk-aac, you can disable features (like, I think, parametric stereo) that have active patents on them.
This leads to the situation where it really depends on what kind of HE-AAC you would like to use (ie. what profile/version, the bitrate, possible regulatory/provider concerns).
Sadly, in most broadcast situations you are likely better off with a commercial encoder that gets the best quality out of your HE-AAC streams due to it including a version of the fraunhofer sdk better optimized for broadcast. AFAICT the fdk code is only open source due to google paying for it to be open for talk interop reasons, this version of the codec isn’t very geared towards broadcast usage.