EPEL-8 modularity was stopped in April of 2023. RHEL-8.8 was released in 2023-05-16 which was after EPEL stopped building modularity packages. So there was no modular packages tied to EPEL-8.8 to be archived. Any backwards compatibility testing using packages in modularity can use what may still work in the standard repository directories (https://dl.fedoraproject.org/pub/epel/8/Modular/) for 8.7/8.8/8.9/8.10. [Whether it works for 8.8/8.9/8.10 is not guaranteed or fixable]

What is confusing then is that https://archives.fedoraproject.org/pub/epel/8/Modular/ exists with packages in it. To be more clear, shouldn't the Modular subdir of https://archives.fedoraproject.org/pub/epel/8/ been removed as of that April of 2023 timeframe?

archives.fedoraproject.org is confusing because it isn't pointing to the archives but to the live site. https://archives.fedoraproject.org/pub/archive/epel/ is where the archives are. I do not know why the site is set up this way.

Due to the nature of modularity, removing the directories would actually cause people with modules installed all kinds of problems and possibly not be able to remove the modules easily. It was decided that leaving them there even if it was with out-of-date software was better than having systems broken.

I suppose that makes sense. I will just disregard Modular for EL versions > 8.7.

Thanks for filling in the missing pieces for me.