The UX just takes you to the default download page for 4.8. The default page shows you the latest version of the framework available for download. It has always worked this way.
The "correct" solution is to update your installer to have a pre-requisite of the NET Framework 4.8 runtime. It should then auto-download the 4.8 runtime, not 4.8.1. How you do that those is dependent on what installer software you're using. If you aren't using any installer software then there isn't a workaround that I'm aware of.