RHS (whichs stands for Rectangular Hollow Section) is a fully enclosed steel column with four sides. The is also thicker than C-Section, giving it much more structural strength.

Steel Hollow Sections: What is CHS, RHS and SHS?

A number of typical simple connections using cleats welded to an RHS column are shown in Figures 6.34 to 6.36. Figure 6.34(a) shows a fin plate welded to the face of the column. The supporting bracket in Figure 6.34(b) can be detailed to be visually interesting.

I can use those with rhs column in which there will be a glulam piece mounted.

https://www.northernarchitecture.us/steel-construction/info-eey.html