BA upgrades

flying BA longhaul for the first time in many many years, in CW with fare class I, and was wondering if I could use some Avios to get one/both legs in F
If I were on VS I know if there were any UC seats free at check-in they'd typically let me do a points (plus taxes) upgrade when arriving to check-in, but I've never tried this on BA
Load check is showing plenty of empty seats in F, but no reward seats availability for my (fixed) travel dates, nor do any seem to pop-up at last moment on flight day
I'm keeping an eye out for rewards availability pre-flight, but if nothing comes up, would I be able to do an upgrade with Avios at check-in? or is this something BA can't/won't do?
I'm only bronze in exec club, not expecting anything special from that
If I were on VS I know if there were any UC seats free at check-in they'd typically let me do a points (plus taxes) upgrade when arriving to check-in, but I've never tried this on BA
Load check is showing plenty of empty seats in F, but no reward seats availability for my (fixed) travel dates, nor do any seem to pop-up at last moment on flight day
I'm keeping an eye out for rewards availability pre-flight, but if nothing comes up, would I be able to do an upgrade with Avios at check-in? or is this something BA can't/won't do?
I'm only bronze in exec club, not expecting anything special from that