Use paint-on supports. Paint them only on the underside of the keystone at the top of the archway (See photo with 3D printer showing the support).
Use "enforcers only" support mode in PrusaSlicer so supports are only generated there.
The model is very large!
Your 3D printer needs to be able to print 143.47 x 206.35 x 237.32
To print faster:
Use the included 3mf file (but change the 3D printer to yours. It may print slower than pictured especially if you have a typical .4mm nozzle since I'm using a .5mm one)
If using a path width of .5 to .6 (Advanced panel in Print Settings tab) you can use 2 perimeters
Combine infill automatically, using 80% (If a percent sign is entered, it will be calculated based on nozzle width)
15% infill, adaptive cubic
Speeds: See screenshot showing preview with speeds mode.
Still takes over 1 day.
See the additional pictures for other printing stats (based on .5mm nozzle).
The author remixed this model.