Depending upon where you live and how long you lay the mower over for winter
General rule of thumb, done for all of my clients regardless of the engine or mower brand
Last mow of the season, change the oil so it sits over winter with clean oil and no crankcase acid build up
Every 2 or 3 years, change to oil filter
In the 15 years I have been servicing mowers I have yet to find one with a clogged oil filter
I like to use 3 yearly because it then becomes every year that is divisible by 3 , ie 2024.2027.2030 .
At the same time change the plugs & check the valve lash .
S for oil it really does not matter all that much
As I keep telling people these engines are crude , rude, & unsofisticated
They are made as cheap as humanly possible so synthetic, semi synthetic , plain , multi grade or mono grade makes SFA difference
I use either strait mower SAE 30 or plain 10w40 and the only oil related problems ever encountered by my customers was lack of it .
They are not bloody Farris Lambouginis or any other exotic engines built with tolerances down to 0.00001" and metered oil flows using carefully calibrated jets to control oil flow to different parts .
As for filters I use only the Stens filters ( Champion OEM spec ) simply because they are the only ones I can buy is a 12 filter trade pack and they are warranted for the Australian regulation 12 months ( because ur government is not owned by the stock market shareholders like the US is ) and that makes the 1/4 the price of mower branded ones .
Even then a lot of B & S motors still ar 100% splash lubricated and the filter does nothing but filter the oil that is splashed around inside the engine when it is in the sump .
There is a big different between Spin on oil filter , Spin on oil filter with pressure fed crank and spin on oil filter with full pressure feed .
And 1/2 witts want to argue endlessly about filter & oil quality as if it made a wrinkled rats rectum of a difference .
I have had engines turn up with the oil so filthy it is a paste and had to be diluted before I could suck it out and those engines are still out there cutting grass.