The reason is because these online sitemap generators are not able to run javascript and store cookies
Since you are on free subdomain
and you don’t have, for example, Wordpress, where you could insert a plugin that would generate a sitemap,
I think the only thing left for you is offline mode
means downloading all files and putting them in a folder
and then create a sitemap on your PC through some program
(search on Google for " free offline site map generator")
and in the settings of that program you tell it to index a specific folder
Then open the sitemap xml file and edit each URL
so it doesn’t show your folders but starts with your domain
https://pokemon-empire-pbs.infinityfreeapp.com/