What methodologies are used for open source projects?

Question

Project management

Open source are completely different, it would be interesting to know about all of them, about their classification. More specifically, we are interested in projects with the following characteristics:
- Long-lived project, average popularity. I mean, there are quite large user stories / epic, which can take from 1-2 man-months (for permanent employment)
- Lack of people for full employment
- The number of opened feature requests / defects exceeds the number of closed ones
- Lack of a clear framework for the release, but constant continous integration, almost any version can go into production.
- There is one main development branch (no support for previous versions - never needed) and several branches for special functionality that is not yet ready.
- The number of programmers is 5 times less than the number of active participants in the discussion of bugs, alpha testers
Current difficulties:
- The implementation of labor-intensive features, since they can take quite a long time, priority is given to what can be done quickly and have a visible effect. In the long run, it has negative effects.
- The number of defects being opened exceeds the "throughput" of the team.
What I found on the Internet:
- Scrum is not very suitable, since there are no clear deadlines, no clear estimates, and there is no clear definition of the team.
- Kanban - I like it because there is a focus of tasks and there are no clear deadlines.
I do not exclude that something needs to be radically changed, namely, to apply a more rigid methodology than what everyone does according to their priorities, but this may not take root in an open source project.