Pixel users report battery drain issues after March update, and this could be the reason
(www.androidauthority.com)
Well, today I forgot my phone in the car when I went into work, and when I came out at the end of the day, it was down to 60%. It's definitely got the bug.
Edit: I checked the battery history and the Netbird VPN app was the highest user, so maybe not the bug. I changed its background usage from unrestricted to optimized and we'll see what happens.