[URGENT] Joomla 6.1.3 and Gridbox 2.20.3 bug

Hi,
I'm working on a Joomla 6.1.3 website and I just ran the Gridbox update from 2.20.2 to 2.20.3 and now I don't have access to Gridbox anymore (See attached screenshot). The Menu in admin panel does not expan no more and when I clic on "Gridbox", I'm redirected to site home page.

Since I've used the Joomla updater fore a couple of versions, I don't the 2.20.2 package. So I can't revert.

Can someone please help to fix this? I must deliver the website this Friday evening. :(

Thanks in advance for the help!