Fixed it on my end, the issue is that MBR holding file havce too many "z" at start so no compatch are working with it.
I just made a copy of MBR for my own use, renamed the file and some bulding to be compatible with COW3

There is no load order, without this patch MGB would never show in game, but with it, as long as it loads after both MGB and MBR both of them should appear in game.

You can try moving MGB + MBR after the GRANDER building compatch (or disabling the compatch altogether) and if that makes the MGB buildings show up again, that likely means the error is on the side of GRANDER compatch.

Just make sure to use a new save, since the lack of existing mods could remove some buildings from existence. Also make sure that you fulfill the requirements for MGB buildings. Keep in mind that the Grand Statue is now much lower in the buildings list, so you might have simply missed it.

Is there a load order between MGB and MBR ?
I don't see the MGB buildings when MBR is enabled.

my load order is

Other mods
building mods
MGB
building mods
...
MedievalArts
MedievalArts - special
COW3
MBR
MGB + MBR
MBR + MedievalArts
...
A Special World (MA, UBP, etc.)
A GRANDER Buidling Compatch (huge holding compatch)