If you mean operational upgrades, I haven’t received any such upgrade in all my years of flying on SQ. The one time I got a free op up to F was on my birthday when flying to JFK from FRA (but this was an unofficial space-available status benefit when flying on your birthday).

SQ’s load factor management is pretty good but I have heard operational upgrades happening from time to time.

Just to add, all things being equal, they would follow LTPPS / TPPS / QPPS, then KFEG etc sequence for upgrades if such a scenario were to occur.

You may wish to check if paid options are available.