GravityMod

This mod allows you to set your gravity to any of the 6 directions, using 12 new items added in the creative mode inventory. Additionally, it also adds a block allowing you to create variable size gravity fields, as well as a item that allows you to adjust gravity strength.

This is the only mod that does this for Forge 1.16.5

It also has compatability with PortalMod, allowing for things like gel, turrets, cube grabbing, and portals to function in all six gravity axises.