(First comment)
Thank you very much HerelsTom, highly appreciated! So according Pcristi I should install 2.1.6 fw first and with the hope that it works. For some reason I can't unzip files with WinRar, Zip 7 or WinZip, but ussualy I just rename the file into "update zip", correct? I will try this out and I really do hope that I can install afterwards the custom firmware. I'm only confused which CFW, because there are a few and I don't know which one also has YouTube Smart tv? ? ?
___________________________________________________________________________________
(Second comment)
I have just tried to update the 2.1.6 version and it doesn't work. I have only the Android ring but after a minute or two HM Q10 Pro just boot up with the 2.1.5 version from 19-12-2019! It looks that it has baked in, and I can't change anything about that. I did this with 3 tumbdrives formatted FAT 32 and it doesn't work. When I plug in de tumbdrive and going to the internal menu "upgrade - Local upgrade" it doesn't recognize any files on the tumdrive. I know that I have to use the paperclip options etc. but it was just to check it out. I think that the file should be unzipped first despite all the discussions at this forum. However I didn't unzip and just renamed the file before copied to the tumbdrive.
However, the HM Q10 works fine with that fw version (2.1.5), but I'm not happy that I can't install apps like YouTube Smart tv, Aptoid or Google Chrome. It also plays everything from my ext. HDD. Actually it is very hard to do anything with that version and it does allow to install apps from the Google Playstore only, including "sideload", but APK's are impossible!
I do hope to get some response about this matter. Thank you all..........