Basic, it doesnt matter if its a 4 stroke or 2 stroke, simple rules
Anything with a catalytic converter in the exhaust uses unleaded
regardless of the CR
Any small industrial or stationary 4 stroke uses unleaded.
Any standard 2 stroke uses unleaded.

2 stroke engines have low compression ratio like 6:1, as do stationary
or light industrial 4 strokes such as generators and lawn mowers at
little more CR than the 2 stroke.

Many 4 strokes in motor vehicles are higher compression ratio by
comparison at avg 9:1 CR, but not all are the high.

If you use leaded in anything with a catalytic converter youll
overheat the converter and kill it.
If the compression ratio is lower than about 9:1 in any engine (such
as those above) and you use leaded fuel the engines will coke up with
large deposits.
The plug will foul sooner and the conductive build up on the
insulator will cause spark leakage and poor plug performance through
most of the plugs life.
(Hard starts)
In the industrial 4 stroke it will coke up the valves, in a Briggs
stratton side valve engine the valves will start clipping the head.

The low CR engine is simply too cool inside and the lead sticks to the
cool surfaces and ends up as a clay brown solid build up that gets
glazed around the exhaust side and ex valve to a hard toffee.