You say the carb is new Walbro LMT.
The Walbro LMT are NLA. (No Longer Available)
If you ordered a Walbro LMT
replacement you probably received a Nikki and if the price is in the $20 range it's a China clone carb. They lead you to believe you are getting a true Walbro but that is not so. (and known for the issues you are having even when new)
Do you still have the original Walbro LMT carb?
The usually clean up really easy and then when re-installed adjust the idle jet.
Here is a link to carb info, repairing, etc.
Just select Briggs and then single cylinder Intek then you will see Walbro and then go back and scroll down to see the Nikki's.
https://outdoorpowerinfo.com/repairs/
Briggs started using Nikki's instead of the better Walbro's is why they are shown as NLA.. (and China clones the Nikki's and wht you describe with your engine is quite common with the Nikki's.
Also do as suggested by slomo and add a Briggs red fuel filter and replace the fuel hose. If no fuel filter is installed your carbs are going to take in trash AGAIN. Also use NON-ethanol fuel.
Just another hint to keep in mind:
That link above WILL NOT do you any good if you are going into a China clone replacement $20 Nikki because it's probably got the wrong jet plus it's just wrong China thing. You just have to suck it up and get another carb assuming the intake gasket at the manifold is good and also the plastic manifold is not cracked.