OK, after I gave up all development for this phone, I can share where I ended.No; I had to set it down for a while, and haven't had time yet to pick it back up. In the meantime I've been happily using stock Sony firmware with both VoLTE + VoWiFi. But I want to find time to start poking at this again. I will probably have to start over from scratch using the notes I wrote here, because I honestly can't remember at this point (after all the time that has gone by) where I left off, or what my workflow was that I came up with to produce a build of 15.1 that has at least working VoLTE. (Though I probably still have a copy kicking around of the 15.1 build I came up with that has working VoLTE, if that would be useful/helpful to you.)
Yes, if you read my other posts, you'll see that I called out how previous builds of LOS for Z3+/Z5 family could never have had working IMS/VoLTE. Kang-ing of Qualcomm IMS userland blobs from Sony ROMs was woefully incomplete.
I realize that at this point Oreo is too old to be attractive to users as a third-party ROM, at least as long as usable Android 10/11 builds exist. Still, I think it is important that the IMS puzzle gets solved on Oreo first, because from what I've gathered, Oreo is the last version of Android that supports the older IMS service APIs without any changes. To continue to use these blobs in Android 9/10/11, shims will likely need to be written. (Either that, or IMS blobs from other phone model stock ROMs that are written for Android 9+ and are also compatible with the MSM8994 modem will need to be substituted in.) But before we get to writing shims, we should make sure there isn't anything else we have missed...making sure it runs in Oreo correctly is a good way of doing that.
According to his changelog he uses different way to enable the camera.
Sad to hear this, real shame the correct sources didn't leak...I felt really mad after discovering, that carriers provide their ims modem settings to device manufacturers, who are either directly program it to modem, or they have a proprietary way to program the modem from OS. Such a waste of time.
I gave up, I'm buying new phone by the end of the year, will do proper thorough research regarding manufacturer provided software for the phone before. Shame on qualcomm !!
The answer is quite simple:
After some weeks trying to fix one of these problems I have to say that I'm not able to do so!