TYPO3 Core

I tried to add new page types. For this i used this documentation.
https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/ApiOverview/PageTypes/CreateNewPageType.html

I registered own icons and used them.
in the page tree toolbar on top i can see the new icons.
but in the page tree itself, beside the paget title, there is no icon (not a 'broken icon' too)

after that i tried it without my own icons. Instead i used typo3 known icons - that worked perfect.

after that i took the svg content from the registered icon and pasted it in a new file and use this file for my new icon.
This resulst in the same behaviour as described above.