Hi @Rubberbrick,
There is no correct answer to this question.
How a system is grounded, whether the AC is floating (not grounded), the DC negative is floating, the equipment chassis is floating, or any or all of them share a common ground (or none at all) will vary depending on the rules, regulations and norms of your specific location and the interpretation of the installer to those.
All combinations work in some circumstances. Anyone presenting some authoritative answer must caveat it with their location and application. For example even in the same region the rules may vary between permanent stationary installations and mobile vehicle installations.
Professional installers will have spent some time understanding their local regulations, their local market and how various Victron products work in making a decision on how and where to ground.
A big part of electrical license qualification work is understanding these sorts of issues and interpreting the rules.
I personally do not ground the DC negative in my systems, but then my local rules require that I have double pole DC isolation and circuit protection.
My AC neutral is grounded, my high voltage PV frames are grounded, and my equipment chassis are grounded (when they have ground mount points). This configuration works well for me, but may be completely non-compliant in another jurisdiction.