Dremel tool with small cutoff wheel.
Cut the nut in half with a vertical cut, or cut a slot on one side of the nut and pry it apart & off. Way easier than trying to drill out the bolt.
That’s hardly stripped. Are you using the right size?
Easy options are vice grips, or the stripped bolt extractors. Should make quick work of that.
If that fails then the dremel method. Start easy.
Perfect job for a Dremel and a cut off wheel. Harbor Freight has a cheap knock off that will work to cut the nut off.
A lot more delicate and less likely to damage the toilet base.
You can also try a dremel tool to cut a slot in the bolt. Then use a screwdriver in the slot to hold the bolt while you try to loosen the nut
Buy a replacement and a few carbide tipped bits up to the diameter of the bolt, and drill it out is what I would do.
Small metal sawzall blade, just make sure the nut doesn’t spin.
Are you trying with hand tools. Sometimes if you use a impact driver to take off a nut that’s stripped it’ll spin it fast enough to spin it off. If that’s not the case I’d use a dremel tool with a cut off wheel and cut it off. Good luck.