Wine Staging, the highly experimental area where all the latest (and often not "greatest") code comes in for Wine testing now has a Patreon so you can support it directly.
It's perhaps not as well known as the normal Wine project or Valve's fork with Proton but it is an important project itself. Containing a set of patches that are applied on top of the main development branch of Wine, the idea is to provide experimental features and fixes faster in a way that users can grab and test that eventually get upstreamed into the main Wine project once they're ready.
Wine Staging is still very much a volunteer project and it's been going for a few years now, as they keep updating patches and attempt to get more upstreamed. They said having this new funding campaign allows them to buy games, software and hardware required for all the testing they do.