If apache24 is build --enable-mpms-shared=all, then all possible MPM modules for the platform are build and installed, but only one MPM module is tracked in httpd.conf. Even If I try to build with explicit --enable-mpms-shared"prefork worker event" it results in having only a line for mpm-event in httpd.conf. Removing event from the list results in a line with mpm-worker. I suspect the last valid mpm module overwrites all others in the DSO list.
With --enable-mpms-shared, --with-mpm=FOO overrides the default MPM but you'll be able to edit the LoadModule directive as desired.
Created attachment 32239 [details] [patch] fix mpm list in httpd.conf
Committed to trunk in r1652930, proposed for 2.4.x (r1652934). Thanks for the patch.
Backported in r1661848. Will be part of 2.4.13