The attached files contain an updated version of the MSFS In-Game panel built using the latest SDK - it has been tested against MSFS 1.27.21.0
And thanks to another PF3 user, goblinrr46 (ju), the icon now displays on the toolbar!
I am supplying 2 versions of the add-on, one is built for Web Display port 7339, the other for port 9000 - the clue is in the filename. The entire contents of the chosen zip file (a directory called 'maximus-ingamepanels-custom') needs to be copied into the MSFS Packages\Community folder as before.
Should you need to use a different port the number can be changed by editing the file CustomPanel.js in the html_ui\InGamePanels\CustomPanel folder. Look for the word 'localhost' (like 'http://localhost:9000' and change the port number (9000 here) to a value to suit your system - it needs to match the value in PF3WebDisplay.ini
I am hoping to customise this add-on to make it more specific to PF3, but that's not top priority at the moment.
Do please come back to me if you have any further issues with this.
Cheers,
Martin
(PF3 Web Display developer)