Hi Fabio,
OK, if I understand it correctly, your browser shows HTML code instead of rendering it.
I've seen that happen before and it has to do with different defaults of different Zope releases with respect to the document content type.
Elder releases report html per default, whereas newer releases don't (and report txt or so).
I've fixed that in November 2023.
Now if you want to upgrade to schedulix 2.11, you'll have to import the 2.11 SDMS anyway.
(you can find the SDMS.zexp in the schedulix/zope4/import directory)
This means you'll get the fix by doing the import.
Everything else is stored in the User or Custom folder and not affected by loading the newer release.
Please advise if the issue persists after importing the 2.11 SDMS.zexp.
Best rgerads,
Ronald