Bookmarked Hyperlinks are no longer working

Harvess I've been working on this for a few days. I have it working in SharePoint Online and M365 with the desktop app (which you need to insert the link).

In the documents that I'm linking to and from, I've set the Hyperlink Base to the SharePoint site they are both in (I don't know if this works if they are not in the same site). Now, when I insert a link, I choose the bookmarked document from whatever works best, in my case, it's Current Folder, then click the button Bookmark... in the dialog box and select the bookmark, then click OK.

The link I've inserted is not absolute, but it starts with the site name from the Hyperlink Base. In other words, there is no protocol (https://) or instance name in the address (but both are in the Hyperlink Base). Instead, it takes this form:

sitename/libraryname/filename#bookmark

Now, when I click on the link in my doc, I get the following warning. After I click OK, first the bookmarked doc opens, then it jumps to the bookmark:

Yay!

Next, I'll have to test what happens when I move one or both docs to a different library. Since the Hyperlink Base is just the site, not a subfolder or library, I predict it will work, as long as the link in the document lists the new subfolder or library, as it does now.