If users are contributing the content of the app, it seems they should have a way to hold the owners accountable.
Alternatively if Komoot was a worker co-op a sell-out would only be possible with consent from the employees. Consumer co-ops (where users can vote too) are also an option but with more caveats.
Unless you already have large interested parties "bribing" (not technically of course) the group of controlling members tends to be a weakness of anything crowd sourced.
Especially since it is rarely cut and dry. If the finances aren't working out is it better to sell and keep the site online or not? Are intrusive pop ups begging for donations a better option? There isn't a singular true best option.
IMO non-profit or charitable status is a must for sustainable, open, community-driven projects. One of the dumbest takes I often hear is "this for-profit corporation was good and kind before financial capitalism came along". Financial capitalism was always there, the for-profit corporation is pretty much a pure product of financial capitalism. Don't believe any for-profit startup that tells you it is all about the social mission, it is not. Even if the company is European.
Easiest? Pay yourself a nice fat salary and use most of the rest of the money to hire “nonprofit management companies” which may or may not be you or your friends in a cheap costume.