I would suggest you book the early-morning flight out of LIN, as it guarantees a connection to all the morning/early afternoon BA flights to North America, so that's the one flight that's least likely to get cancelled. I noticed that that was the case with the early-morning FCO-LHR flight whenever the COVID cutbacks hit. Also the first FCO-LHR flight in the morning is the one flight that rarely has Avios availability, as it's always very busy with connecting traffic. I'm sure the same applies to the LIN flight. In any case I suspect that by March the Omicron impact will have abated and BA will be looking to add flights rather than cancel them.