Yes..ethanol can be bad news in older outboards in particular.
We had an old motor at our cabin years ago ..and because of fuel line issues etc always used non-ethanol gas…but apparently nephews/in laws being nice were filling tank with ethanol blend.or mybe even 85% stuff .and eventually a gas line or gasket failed (due to that I think) ..This happened while I was out on the lake with it..and motor caught fire!
Gas/oil floats on water so it was tricky putting it out w/water..so eventually had to smother it with my life jacket….Motor had external tank fortunately so got gas line off.. Since then weve tried to replace all lines/gaskets etc on old motors with alcohol resistent stuff..

The other problem as noted is that ethanol absorbs water..and it can accumulate in a gas tank..eg during storage. Apparently this has happened in some snowmobile tanks..Some have small displacement high compression engines and when owners ran motors enough water got in combustion chamber and being incompressible fluid basically broke pistons etc on the compression stroke ..(they may have been using 85% ethanol stuff tho..)

So….I generally try to avoid it in even my newer outborads..(tho I have plastic tanks..I think they are polyethylene or something similar ie other than fiberglas)..but getting hard to find non-ethanol gas..(new rules)