The wagtail.contrib.modeladmin app has been removed. If you wish to continue using it, it is available as the external package wagtail-modeladmin.
wagtailsvg/wagtail_hooks.py does import from from wagtail.contrib.modeladmin, so that code doesn't work in Wagtail 6.0.
The quick fix is just to add a dependency to wagtail-modeladmin and change the import to from wagtail_modeladmin .... The better fix is to use snippets instead.
As stated in the 6.0 changelog,
wagtailsvg/wagtail_hooks.pydoes import fromfrom wagtail.contrib.modeladmin, so that code doesn't work in Wagtail 6.0.The quick fix is just to add a dependency to
wagtail-modeladminand change the import tofrom wagtail_modeladmin .... The better fix is to use snippets instead.