I'm afraid I can't answer your question about pre-flight dining other than to confirm that there is still a small area in the lounge with a sign that it's for F dining. As of last week Sunday, the regular buffet was decent enough and the seating area tables still had QR codes for an online menu that listed the burger and a few other items. I didn't order anything so can't confirm if they were actually available. AF and EI also use the lounge but it didn't seem very busy before the 1740 BA flight when I was there.

Something important to keep in mind is that there is no dedicated TSA pre-Check line for the BA gates. The priority security lane should get you to the ID/BP checkers quite quickly but once there you have to join the back of the regular lines for the scanners. There was one new scanner in operation (second machine from the left - available for all to use) so if you are keen not to unpack electronics and liquids make sure you enter the queue for that one after the ID/BP check. With a pre-Check BP you can then also keep shoes on and use the regular metal detector. Not sure if they have a pre-Check card to give you if you have a digital BP so probably best to have a paper BP in hand to show if you want to use the walkthrough metal detector.