I have not post processed (PP) yet completed BIF captures due to still adjusting to my new contact lens prescription with astigmatism. Had a cataract procedure last summer and new contact lens prescription about 2 months ago. While I resumed BIF shooting 1 week after cataract procedure )for distance), I was not too comfortable yet with close up work like viewing monitor for PP until a few weeks back but with using reading glasses. Just for web browsing, no need for reading glasses but when trying to detect noise and sharpness while in PP (longer time with the monitor), eyes easily get tired. It is getting better now and soon will resume PP. I was previously using the FE100-400 with the A7IV and had posted some BIF results here some months ago (just search for gil's posting).
Meanwhile with regards to the RX10IV, I tested this one in 2017 for a few days and should be BIF capable. It could follow small/medium/big sizes birds in my area; and slow/ predictable/bit faster flight as sampled below. Bonus was for some landscape if needed.