Beams can only show their contour lines (edges) and/or their reference line.
The line style for these can be controlled (solid or dashed, etc.).
The contour lines will give you the true shape of the beam - or do I mis-understand what you want?
Unfortunately there is no cover fill for a beam like there is with a slab.
This has been wished for many times - still no sign of it happening.
Barry.
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10