This mount meets following needs.
PLA+ filament is recommended. Tested with Overture PLA+.
Umbrella having a detachable handle with M14-1.0 thread, eg. Uniqlo one. (and most Japanese umbrellas)
1x L bracket like this having 2x M4 thread holes on the side 19mm apart.
Amazon.com : DSLR Camera L-Bracket Vertical Horizontal Switching Tripod Head Quick Release Plate Arca Swiss Compatible with Digital DSLR Camera Stabilizer Tripod Monopod Canon Nikon Sony DJI Osmo : Electronics
2x M4 20mm bolts.
This model uses this great custom screw library.
Custom Threads with Fusion 360 w/ Tolerances by Hawking - Thingiverse
The author hasn't provided the model origin yet.