At this moment we don’t allow setting the id attribute on user provided HTML/Markdown to prevent interfering with site functionality.
I mean, even the autogenerated IDs would do just fine.
If you’re referring to the ones that look like id="community_edit_post_3993740", note that the number will change every time the page is rendered.
For project pages, we do provide some default anchors to help linking to common parts of the page.