There is an issue I just found with Pro 3.5.2 (and 3.5.5). Opening a script tool in Pro, will open the script in Notepad, if using a script within an .atbx. If you are using a Python Toolbox script tool, IDLE opens, as expected:
It may be a 3.5 bug as IDLE is clearly installed?
What are your project settings in
Edit script tool code—ArcGIS Pro | Documentation
first section may apply to your case
Hi Dan - so the challenge is this needs to be globally set as I am admin for about 2000 users. I can probably change my Script Editor py IDE resource, but I don't believe I should have to bake that into the registry, if there is even a registry entry for this. With Pro 3.3.6, by default of the install this all works as expected.
Ryan, it may be baked in at the machine level if python is installed elsewhere and not associated with Pro. That I can't test and you would have to try a few installations. We used to do one Pro image and deploy it to all machines at my university but we did that since we wanted to use a specific python IDE and not use idle or notepad or notepad++. You may want to tech support this issue since I don't see anything on the public facing support site
Good luck,
ADDENDUM
found this BUG-000178804 for ArcGIS Pro
Thanks Dan. Appreciate that Addendum! I do similarly in that I install on two diff masters and deploy out to end user desktops via Citrix. PyCharm always throws a wrench in to installs with ArcGIS, so wondering if that hijacked something when installed.
I used Spyder (now and in my working days) without issues. Narrowing down a specific IDE system issue could be problematic, but worth a look.