Some advice I would give to open-source maintainers, based on my own experience and also advice I've received from veterans:

- take breaks. go AWOL for 2 weeks. it clears the mind

- ask the user to provide a test case to reproduce. if they cannot, close the issue after a month or so

- mark issues as "needs test case" or "has test case"

- use email instead of GitHub notifications. mark as read, labels, folders, etc. are all invaluable

- if some user is abusive, cut them out immediately (e.g. ban them from the GitHub org)

- do a little bit every day so you don't become overwhelmed

- set up automated tests that run for every PR. projects without tests are impossible to maintain.

Good luck!