Probably best to let it rest indeed until a future update fixes things....I'm no Linux Guru but I don't mind fiddling around with it, which can sometimes have an adverse effect. On a positive note : at least the public key issue was fixed .
Well, if apt can't get to those headers, neither will the install script from TrendTech. One more thing I fiddled with is the /etc/apt/sources.list.d/raspi.list file in which I think I uncommented the three repos. Could you try uncommenting those, re-run a sudo apt-get update and then try again with the rasberrypi-kernel-headers (or go straight for the TrendTech install process which does the same thing at some point)?
Hmmm...ok you should try
1- sudo apt-get update
2- sudo apt-get install raspberrypi-kernel-headers
3- run the TrendTech command to install the drivers
If this still fails, maybe there's a repository to point to (I remember I uncommented the "sources" repo in the /etc/apt/sources.list file - using midnight commander and its integrated editor that I had previously installed with sudo apt-get install mc and run with sudo mc. Great little clone of Norton Commander from the good old days of Microsoft DOS ^^ )
BTW after all your updates are you still in 5.10.17 or have you moved up to 5.10.52?
I had an error that was a bit similar. The TrendTech program was trying to build kernel modules for kernel version 5.10.52 but my Stellarmate was in 5.10.17. Updated the packages (Menu-->System Tools-->Package Updater) and then everything went smoothly.
What's your kernel version? ( uname -r )
Taking the public keys from the Ubuntu keyserver works.
sudo apt-key adv --keyserver keyserver.ubuntu.com 494 --recv-keys 04EE7237B7D453EC
To be repeated for each of the three key IDs that show up in the error message.