Next week, It would be great if we could all spend some time in the various GitHub issue trackers and pull request lists. Main question you should focus on: is this issue or PR still valid and relevant for Plone 6? It is okay if you also check if it is valid for Plone 5.2.
For earlier Plone versions we really are not going to do any more fixes, so for me it would be fine to close such tickets with a friendly message. I have written a bash script that may help here, with some options for showing issues on the command line, going through old issues and offering to close them. Here is an example of an issue I have closed with this script. It is a new script, please be careful if you use it. 
And tell me about possible improvements by adding a comment in the script repository.
As for a sprint: this is more ad-hoc than really official. But let's see what we can do as self-organising community. Feel free to edit this post, if you have the rights for that.
My suggestions:
- Take a few hours on Wednesday August 24, any time of day.
- Go to the Discord app, find the Plone community and enter a channel. There is a #classic-ui channel, a #frontend-volto channel, a #documentation channel. Or perhaps the #sprint channel is better for everyone. Most of those have a video channel too, if you want. Check the message in one of those channels to see what people are working on, so no double work is done.
- Pick a plone repository to work on, and announce it in the channel. For repositories like CMFPlone with lots of issues, say which range of issues you will inspect, say 2800 to 3000.
Here are some links to help you find something to do:
- https://github.com/issues has your own issues! Are they still relevant?
- Same for your pull requests: https://github.com/pulls
- You can tweak the search parameters. For example, here is a list of all open issues and PRs in the plone organisation. Current count: 4098. Let's see how many are left at the end of Wednesday!
- 755 issues on CMFPlone
- 527 issues on Volto
- 200 issues on documentation
- 2 organisation-wide projects
- 7 milestones in CMFPlone, including Plone 4.3. A lot of issues in these milestones can probably be closed. Or otherwise moved to a different milestone.
So what do you do when you look at an individual issue or pull request?
- If it has not been updated the last few years, or is clearly for Plone 5.1 or earlier, close it with a friendly message. Maybe add a tag "wontfix" or "25 status: deferred".
- If it is more recent, check if it is still an issue in the latest Plone 6 beta (or the coredev buildout, but only if you are already familiar with that). Report any findings. See if you can add some status tags.
- If it seems an important issue that we really should fix before we create a Plone 6 release candidate, add the issue to a list. I don't really know if milestones or projects work better.
Note: when you close an issue, you can click on the down-arrow and choose 'Close as not planned'. that is nicer than 'Close as completed':
If you are tired of reviewing bugs, you could always switch to working on the documentation or translations.
Note: I would like to create a Plone 6 beta 2 in the last week of August. Maybe the end of next week, if things look stable enough.