Do I need a new toilet?

So, I have a toilet in a 2nd bathroom that has given us some issues on occasion. Most of the times its working good, but sometimes it has overflowed. It has overflowed when both solid and liquid waste are deposited in it. I have a water alarm on the floor near it that has come in handy several times now. When the alarm has gone off, the water is still running an overflowing. We have to shut off the water line to it to get it to stop. I don't want to have to rely on this water alarm & would like to figure out what is going on here.

Therefore, I pulled the toilet to see if maybe something was stuck in it. I got it outside and looked. Nothing. I have a toilet snake device that I used and it goes through cleanly. No issues. I also checked the line in the floor and don't see any obstructions there either. Used the snake in the floor and it didn't seem to get stuck either.

My only conclusion right now is that maybe the design of this toilet is so outdated that it needs to be replaced. Its from when the house was originally built in 1999. Its a Kholer brand. Not sure of the model, but here is a picture.

Any thoughts on what may be going in here and how to fix it?

If it was still running, I mean water was still flowing it could be a combination of things.

You could have a partial stoppage downstream. if you can get a garden hose and run water into it for a while to make sure you don't have a stoppage downstream.

What may have happened is that the flapper hung up on the toilet after a flush. The water continued to run for awhile which eventually filled up the drain line. You turned off the water and the water drained out.

Kohler is a good toilet . That what we normally sell. But if you look at he way it drains to the outlet it has a short flat spot. That is by design but also where excessive waste can hang up.

here is a picture of my Half A$$ toilet. I sliced this Kohler up a few yrs ago.

Check it with a mirror and make sure the passage it not coated with minerals that maybe have coated the passage way. needs to be clean and smooth.

your toilet should not be running, if you did not pull the handle.

if it is still running your flapper is letting water get buy,,fix the flapper.

as far as your toilet overflowing. have a plumbing co rod your drain out

might as well have them fix the flapper also