Recently, while working on a book, I needed to take screenshots. I was moving across multiple devices and working with other authors on this project, so it was important that all screenshots be taken from the same window size.
As long as you close all of your Edge browser windows, you can fire up a new instance with command line parameters that will configure it for you.
msedge --app-shell-host-window-size="1280,1024" --window-size="1280,1024"
If for some reason your path or environment variables aren’t configured correctly, you may need to use the full path to Edge:
"C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe" --app-shell-host-window-size="1280,1024" --window-size="1280,1024"
Since Edge is based on Chromium, you can use most of Chromium’s startup parameters. There are a couple that need to be switched out (for example, references whitelist and blacklist are changed to allowlist and blocklist), but overall, you should be able to use the list of named parameters here: https://peter.sh/experiments/chromium-command-line-switches/.