BuzzPCSOS Do other Bluetooth devices work with your Plasma laptop?
Thanks for your comment. Yes, in fact, I use Arteck keyboards (best I've ever found), so bluetooth from the same company works well. I'm pretty sure my Latitudes support BT5, because that's the requirement for the Logitech Triathlon mouse I've used for years (3 channels needed for the multi-device feature). I did a firmware update yesterday, so today I'll try again to see if anything improved.
In this case, I rather suspect it's KDE Plasma 6 still having some issues that need to be sorted out. The new mouse works fine with my Windows 10 media machine, and with my Samsung smartphone, and both of those are happy to connect in less than a second. And Plasma 6 still has some other oddities. I'm hoping those get fixed soon.