How to stop window enlarging by itself?

Since updating to Sequoia, windows in applications on my mac keep enlarging to near full screen (27 inch studio display), which is very annoying. I can't see what is causing this or how to stop it. It may be something to do with how I'm moving the mouse, but I don't know what and it regularly happens. I've looked in system settings at displays and accessibility, but can't see any settings there that may control it. Anyone know how to remove or stop this disruptive feature?