As the error message suggests this seems to be a type error. So to find a possible cause for this error I followed the traceback down to
/var/www/nextcloud/apps/dav/lib/Connector/Sabre/FilesPlugin.php - line 356:
That is:
$propFind->handle(self::SIZE_PROPERTYNAME, function () use ($node): ?int {
return $node->getSize();
});
Here, somewhat simplified, Nextcloud seems to request the size of an object and expects this property as an integer value while getSize() returns a float.
Consequently I changed the expectation from ?int to ?float just to see what happens… Reloaded the tab in Firefox—et voilá: my home directory is available again. Maybe these hints can help.
Please note, that I didn’t do any deeper investigation (,yet) so maybe there are side effects which don’t jump up on a quick glance: let’s see, what the developers work out 