For example Krita. https://krita.org/en/download/ FOSS but you can buy it on Steam, Microsoft Store, Epic Store, and Apple Store. You get one exclusive feature, automatic updates (and more recently Steam Cloud sync support), and you also support the developers (on the other hand Valve, MS, Epic, and Apple also gets a cut too).
If you read for example the Steam reviews everyone points out that it's a free software but buying on Steam is also a good and very importantly straightforward way to support the devs + the platform itself has such a pull ("buying games you never play") that people buy it just for the case of having it in their library