I too have been having problems with pairing bluetooth but for me it’s with my android xaiomi note 6 phone. I did get it to work before with the keyboard before I upgraded the firmware but I’m not sure that’s related. I also tried pairing with my Linux Mint that fails also. like you I see the blue light blink slow but I see no devices listed on my bluetooth device I’m trying to pair with. The Linux Mint is version 19.3 Tricia.
I saw another person that had the same problem with apple IOS and he was told to try this to unpair the device: http://guide.sensel.com/morph/#unpairing. I went ahead and tried that on my android and now at least I get as far as seeing the morph listed on my bluetooth screen. but attempts to connect now seems to fail. But at this point I don’t have the keyboard overlay installed so that could be my new problem. I have a custom linnstrument simulator running on it now that’s not easy to remove so I’ll try it again later when it can be done.
Update after it seemed it would never connect I closed and reopened setup and now I note that the morph is now paired after doing the unpair above, but I don’t see any midi devices listed in my android synth app called DRC. so maybe bluetooth midi is not working yet on this android?