Opps. sorry. Didn't realize the object was two boards.
I didn't see an option in the parameters to turn one off... so you could do it with SEO (Solid Element Operation) workaround.
Use the slab tool to draw a "box" around the board you want to eliminate.
In SEO, Select the Skateboard object as the "target" and the slab as the "operator". Use "subtract" as the operation.
Hide the slab's layer.
Select and view the skateboard object in the 3D window (Parallel projection settings-Viewed from the top).
Go: File> Libraries and Objects> Save 3D model as...... "an object".
Maybe easier to look for another board?
Marc Corney, Architect
Red Canoe Architecture, P. A.
Mac OS 10.15.7 (Catalina) //// Mac OS 14.5 (Sonoma)
Processor: 3.6 GHz 8-Core Intel Core i9 //// Apple M2 Max
Memory: 48 GB 2667 MHz DDR4 //// 32 GB
Graphics: Radeon Pro 580X 8GB //// 12C CPU, 30C GPU
ArchiCAD 25 (5010 USA Full) //// ArchiCAD 27 (4030 USA Full)