How to position a specific window at startup using Gnome-shell?

I'm running Ubuntu 21.04 and Gnome-shell on X. I have several Startup Applications configured in Gnome Tweaks, but how to control their window positions? This one-liner in a bash script does just what I want with Thunderbird for example:

xdotool search --name "Mozilla Thunderbird" windowmove 0 0

The question is how to get that script to run when I log in. Gnome Tweaks won't accept my script files as startup apps, and other places I have tried (e.g. .profile) seem to be run too early. What would be a place to put a script file to run when Gnome Shell has done its startup job? Or maybe a different solution altogether? Thanks :)

That is the function of GNOME Shell extension Put Windows.

Within the App, you can configure window performance by adjusting some simple settings.

For example. I use this for Firefox to position the initial FF window to the left of my monitor extending top to bottom and approximately 66% across the screen. Use of Keyboard Shortcuts gives even further control of windows and combined with Startup Applications places windows in the postions you want them.