I discussed this with a customer recently. They asked for advice because the change in search behaviour is having a detrimental effect on their success metrics. They want to feed agentic search with legit and up to date information about their product, but ungating it has tanked their sign up rates. Here is an abridged version of my thoughts.
I believe un-gating is the right move if you are optimising for growth, in which case you should be measuring and gauging success based on reach.
Have you read Before You "Build a Community," Decide: Library or Coffee Shop??
I would take this as an opportunity to change how you measure and communicate ROI. If you stop thinking of your community as a coffee shop and start pitching it as a coffee shop inside a very successful library, you might be able to paint a different picture.
If you take that approach you can start reporting the community as a funnel, measuring reach (search impressions) and value consumed (accepted answers viewed). Then you should normalise participation numbers when you report e.g. new contributors per 1,000 organic visitors. If you just report raw numbers they will be harder to interpret as you un-gate content because the denominator changes. If more anonymous people can consume content without registering, new registrations and MAU may drop even if the community is providing more value than it was.
We have Gated Topics in Category but I wouldn’t gate solved support content or evergreen troubleshooting topics. That is the content most likely to win SEO/AIO reach and deflect support, as well as building trust with new members.
Your observation that closing Announcements helped with traction is useful info to have. Based on that I’d gate product and company-value content like announcements, release notes, news, roadmap, Ask [company] Anything etc. You could try some other traditional engagement tactics in private categories too. Live AMAs, QA roundtables, career clinics, office hours, that kind of high intent programming that is worth signing up for (or at least enough to get people curious).