The solution is the following:
→ put it inside a container
→ in the left sidebar set the container “Size” to “Advanced Settings”
→ this will automatically apply a CSS-Grid, so go down to Layout>Advanced CSS Grid
and twirl open the Rows(1) submenu by clicking the little black triangle to the right
→ this will reveal the culprit: Row height is set by default to “min/max”
→ press on it to reveal the submenu and select “max content”
->PROBLEM SOLVED
(I know it’s cumbersome that this essential feature is hidden under 2 submenus, and I already asked Wix to move it to a more easy accessible/visible location in the menus!)
I really have to thank Vanja from Wix support (Product Support Specialist) for pointing this solution out to me!