The common wisdom is support or chamfer instead of fillet. This is 100% the only solution.
But wait!!! you can also do a nuanced combo if you want a more fillet-y look.
Make a chamfer that is at least 35-40 degrees from level. Have that chamfer rise to the point that an equal fillet would be curving past 40 degrees, then go into a fillet curve.
This way, it look like a fillet to a passer by when it is sitting on a surface, but has a chamfer at the very bottom that is steep enough to not need support.