I honestly think this whole "mobile network standby" is overly inflated and incorrect in what it reports.
Last night it says that I used 40% for each individual hour overnight, but had no actual minutes used to where it would have contributed to such a high number. If that were true my phone would be dead by morning.
It also said I used 31% for 4 minutes today, yet my battery level stayed the same.
On my work phone which is a pixel 4a, it says I used a few hours worth with 1% drainage.
Again, I think the number is bogus and incorrectly being reported somehow. It's causing a lot of stress for some people to which they focus on it too much, but I understand for some it can be a legitimate issue.
With the latest February patch it hasn't been as high as I'm used to seeing it, so I'm not sure if that's carrier services or the s/w being improved.