@rinigus and @mautz, a hugh thank you to both of you. So, I installed OKBoard as mautz suggested and it's quite a revelation. As for presage, I read the packaging instructions and it's quite fascinating. Yet, I have a feeling this process might be beyond my abilities (for now).

Could I just bring up a few things I noticed? Maybe someone could help me with some of these, which would be highly appreciated.

1) When I connected the previous incarnation of the phone (Nexus5/CM12/SFOS2.0) to the car's "multi media system", the phone would normally send the address book automatically. Now (CM13/SFOS2.1.3.7) I get a "device connected - transfer failed" instead. No big deal, since I can always send the vcf file manually (BTW, A2DP audio works flawlessly, though). Which brings me to...

2) I am sure there used to be a "share" option in the file manager (to share via bluetooth or email). I cannot seem to find that anywhere. Any suggestions how to get it back would be appreciated.

3) When I used to type a text message, I got a counter giving me the number of characters left for that text/SMS. That seems to be gone. Is there are way to retrieve it?

4) Upon opening the case, the phone used to come to life (display lit up faintly), so I could double tap it to wake it up. Now, there is no reaction to opening the case, thus, I have to press the power button. No huge problem, but maybe it's just a setting. So, I thought I'd ask.

[5)] As for the broken audio on bluetooth phone calls, someone suggested to me that this sounded like an "endian" problem. Unfortunately, I couldn't get any further information. Has anyone looked into this issue?

Sorry, this ended up being rather a lot.