1. The oils specs are the important point. Check the API S* (or ACEA) specification requirement of the engine manufacturer.
2. Buy anything which is API S* or better, covering the SAE 30 viscosity range, either a simple SAE 30 or SAE 10W-40 or whatsoever having the 30 within its range.
3. Earlier I also used to buy extra lawn mower engine SAE 30 oil bottles. Nowadays I take the oil from my 20 liter can for my cars for the lawn mowers also. It is an API SL oil SAE 5W-40. The price/liter is lower than the price of the "lawn mower oil".
4. Commercially sold "lawnmower" oils are e.g. Liquimoly API SJ, CASTROL Garden, 4T 151B50 is API SJ, MANNOL SAE 30 4-Takt Agro is API SL, Motoröl MOBIL GARDEN 4T SAE 30 is even only API SG. So you probably have an oil with higher specs already at home for your cars which probably is cheaper and also is suitable for lawn mowers engines.