Hello there! My apologizes for being silent for a while - I was quite busy. I checked addon with absolutely clean setups of Blender 4.2.0 (when extensions platform appeared for the first time) and Blender 4.3.0 - it works perfectly as intended to. So I believe that there is something wrong with particular blender instalations or may be some kind of obsolete settings, dragged from version to version for years, or may be even some kind of interference with other addons.
Thank you for this very useful addon.
There seems to be a small bug in Render Overscan: It installs correctly when installed , but doesn't show up in Properties > Output in my Blender configuration, probably due to a leftover string from previous work, overlooked for deletion in init.py line 27.
Temporary workaround for users experiencing the same issue:
Default path Windows: c:\users\username\AppData\Roaming\Blender Foundation\Blender\4.2\extensions\user_default(install from disk) or blender_org(online installation)\render_overscan\
Default Path Linux: home/username/.config/Blender/4.2/extensions/blender_org (online installation) or user_default (install from disk)/render_overscan
Open the init.py file with a text editor, comment out the line 27 (bl_parent_id = 'RENDER_PT_format') adding a hash (#) at the beginning, so that it looks like: #bl_parent_id = 'RENDER_PT_format'
Save and close the init.py file and restart Blender.
The Panel for the addon "Render Overscan" should then appear in Properties > Output, under the name "Overscan Settings".