I have an older Honda HT-R 3009. It starts fine but when I put it in gear it quits. Just used it last week to cut the grass and went to use it and now it won't run when I put it in gear. The problem just started.

Sounds like carburetor problems. Engine dies when it put under a load

A couple of things could be going on. If there is a bad ground on any safety switch that can kill the engine.
Or
If its not puffing or smoking then its running to lean

Check fuel filter and needle and seat valve. This is what's regulates the amount of gas in the bowl. If that's a hair to low then its running lean on the get go.

Dirt in carb at needle and seat and crab bowl will cause this. Use carb clean to clean it all out.