As Xeno and cobnut said, there’s no easy answer to this question. Some filaments, like CooperFill can achieve dramatic overhangs because of the material properties whereas ABS is much more finicky about it. In general, an overhang of 45° is considered the point where support will be needed, but printers with active cooling (extruder fans) can do upwards of 55°. You can try going this high as a starting point, then dropping it down if you get too much curling/noodling/drooping.
If you have a part you don’t want to use support for, your best options are trying to reorient the part or printing with dissolving support (if you have dual extrusion capabilities). Orienting models for printing is as much of an art as a science, so this does take time to learn. If you have the ability to print dual material, soluble supports are fantastic. You just print the part in whatever material you want, and print the support in a material that can be dissolved away after the print is done (water, d-limonene, etc.). PVA is a bit tricky at first (use this to support PLA), but HIPS (used to support ABS) is a great material and I can not recommend it enough.