Motor starts for a few seconds and dies.
Excellent. This tells us the carburetor is clogged and the motor is not getting fuel. We are almost there. If you want to go a bit further you can clean the carb and you will be happily cutting grass again.
Unfortunately the carb is very close to the mower deck thus making it difficult to work on while still attached. It doesn't need to be completely removed, just enough to tilt it to access the main jet inside.
Maybe first take some pictures or a video of the carb and all the stuff connected to it so you have a good reference on how it all fits together.
Maybe the first thing to try is to see if in fact you have fuel in the bowl. You can do this without removing the carb. Take a thin marker and make a line from the top of the bowl up to the carb. This marks the position of the bowl in relation to the carb. The bowl is fairly uniform on this carb so it probably won't make much difference but I always like to put things back exactly as it came off.
Turn off the fuel supply valve. Take a shallow small container that can fit between the bowl and the mower deck, perhaps a small pie plate and undo the screw on the bottom of the bowl and see if fuel comes out. If it does then chances are the needle valve on the float is working properly. To test this further open the fuel shut-off valve to see if more fuel comes out, then close it again.
If all is working to this point then the carb is getting lots of fuel from the tank, it is just not sending any to the motor, chances are you probably have a clogged main jet and you will have to loosen the carb to angle it to get a screw driver inside.
We are almost at the end and I am not sure if you are comfortable going further. The only issue we might have is that you need the proper screw driver. It is a regular flat head one but you may need to grind/file the shoulders off of it so it fits up inside where the jet is.
Try testing up to this point, let us know if the fuel supply is good and if you want to continue.
We are all here for you and will help you through this if you want. Let us know.