Depends on the quality of the oil. A cheap mineral oil might need to be run at 20/25:1, whereas a fully synthetic race 2 stroke oil could be run at 50:1 or leaner. Don’t make the mistake of thinking too much oil can do no harm, IT CAN ! it won’t flow as well through the tiny orifices in the small carbs like on strimmer’s, and can cause a weak mixture and seizing.
My secondhand strimmer has 20:1 molded into the filler cap, I run it on high quality racing 2 stroke @ 50:1 (for over 20 years) and its running as sweet as ever 😉