I've added more years to the forum search in the next update so you're not restricted to 1y max.
We're skipping across a lot of issues here:
should it be the community to carry the burden of customer service?
No, but the forum is a nice to have that pretty much every other game making software has. It's an extra you are not obliged to use.
Ofcourse, without a thriving community, when the manual would be lacking
This is as far as I am aware, up to date. Note, manual is NOT for "how-to" guides it's a very specific document documenting features in Construct 3.
Which manual entries are missing?
The Construct Team should tend these forums with TLC.
Search could probably be improved, what else needs TLC in it?