Mounting a TV above a fireplace, even an unused one, is a victory of aesthetics over viewing optimisation (IMO). Have you considered a Samsung “Frame” TV. It will double as a painting when not in use as a TV.
I see someone above prefers the LG interface to the Panasonic, whereas every member of my family prefers the Panasonic! (Our LG is just an LCD, but it still has the same magic remote as the OLEDs). I get that some find the interface on our Panasonic OLED too basic, but it just does the job it needs to without getting in the way. Some people love Android TV, whereas others loathe it with a passion.
My final comment echoes one made above - is it really necessary to put the tv above the fireplace? I have rarely seen this work, as it typically creates inappropriate viewing angles (and sore necks!). What height will the base and top of the tv sit from the floor if mounted above the fireplace? I’ve seen tvs put above old-fashioned fireplaces (with a high mantelpiece) like the one here in my lounge, and looking at the tv in this room the top of it sits lower than the base would it it were mounted above the fireplace!
Mounting above the fireplace was also not my first choice, but due to the lounge layout (incl wall plugs etc) and the wife preferring that layout, it seems like it is the way to go.. I have not measured the height per se but will try to get my sofa moved first thing post lockdown as I can't lift it myself unfortunately and then will reassess the viewing angles.
I've only ever grown up with a panasonic plasma and parents later bought a LG LED TV (LB650V I think) with WebOS, what surprised me was that the current Panasonic offering still offers very similar OS to what my plasma was like, and the WEB OS feels very intuitive, which is why I do hope the C9 goes down in price... but it hasn't.