Thanks, Tivoburkee; that would explain why things worked for the Premiere, but not for the SS+, and would predict that they would work for the Express.
A couple of flies in that ointment, though 😢
Firstly, the LG Magic Remote is a dual RF and IR device; it talks to LG TVs via RF as standard. So it could perfectly well talk to the SS+ via RF, I would have thought
Secondly, the list of supported devices, as shown by the setting dialogue on the LG TV if you go to manual, includes the 3810; why would it be there if LG didn’t think they could control the SS+?
(I am, though, presuming that it says 3810 rather than 3810X, as there is a whole family of 3810 variants, and it will control them all; certainly the X is the most widespread and plain vanilla variant, I think, so I would expect it to be included).
Finally, though it is not an objection like the two points above, what has whether these devices have an HDMI port or not got to do with anything?
But I am still learning about LG TVs, though I have had Roku devices ever since the 3, so your guidance, as above and on my difficulties with it, would be very much appreciated.
[Edited to get the model numbers correct - thanks Tivoburkee ]