It's probably unlikely that UA will put you on a SQ flight, even with the MOU
https://www.flyertalk.com/forum/unit...-airlines.html
https://www.flyertalk.com/forum/unit...fly-sin-2.html
Uniteds sfo-sin is going to be on the VTL list starting 1/5/2022. It operates MW F Sa in jan and Feb.is your current flight not on these days? Call United and rebook on MWFSa
https://www.flyertalk.com/forum/33746852-post168.html
(It was scheduled to be daily starting Feb 11, but now it's daily starting March 4(which can change)