It happens to me as well.
My xs max battery only lasts for 5-6hours screen on time. It was 7hrs+ on 12.1. I did wipe my phone and restored the iOS thru iTunes but nothing has changed.
I noticed that if I use it continuously, the SOT might be longer (for now is 4 percents for 52 minutes on safari, last charged about 90 minutes ago). But on normal working days, if I unplug it at 8am, slightly use for about 30 minutes, it would be down to 90% at noon. From then until 3pm with 1hr on safari it would be around 70%.
I use it with AW and connections alway on.