The link generated include a string such as /hrrmc-mp?view=article&id=657:hrrmc-site-plan&catid=101:hrrmc-facility-mp, rather than an SEF URL.

Did you create the link using the JCE Link dialog? Is it to an internal article on the site?

Do you get the same link if you use the Article button below the editor to select and insert the link?

from JCE link dialog: https://www.rtaarchitects.com/test-article-links?view=article&id=657:hrrmc-site-plan&catid=101:hrrmc-facility-mp
from article button: https://www.rtaarchitects.com/test-article-links?view=article&id=657&catid=101

These links are essentialy the same, th eJCE one just includes the article and category alias in the link.

It looks like an issue with the routing. Is this link associated with a menu item, either directly or by category?

It worked as an SEF in J3. So, it may be that J4 has a different routing structure that I wasn't aware of.

Is it the same htaccess file as the J3 site? Perhaps J4 SEF requires changes to the htaccess?

I have discussed this issue with another experienced Joomla extension developer, and wer have concluded that the strange SEF URL conversion is the result of the new SEF routing in Joomla 4. As SEF urls are created with reference to the alias of the menu items the article is associated with, if the article is not assigned to a menu, then a SEF url cannot be created (the SEF url is not created from the article/category alias).

One solution suggested was to a revert to a Joomla 3 style of SEF URLs. To do this go to Content -> Articles and click on the Options button, then on the Integration tab, and set the Remove IDs from URLs to No.

Another more complex solution, but one that guarantees full SEF urls, is to create a hidden menu and assign the articles to it. The menu would not show up in the site layout, but would create correct SEF urls for each article assigned to it.