Downloading previously purchased launcher

My son just got a new Windows laptop. I tried to install the Java version of Minecraft. We purchased Minecraft years ago. I was not permitted to download the program until I migrated his account to Microsoft. I did that. If I access Minecraft on his old laptop using the migrated accounu, everything works fine.

Back to the new laptop. I go to Mojang.com and follow the instructions for downloading if you've already purchased. I select the computer version and then Java version. The launcher downloads. When I try to open the file to install the launcher I get a dialogue box with the following message: "Check your Account Minecraft Launcher is currently not available in your account." Error code: 0x803F8001.

I have googled this message and completed the 8 most common fixes. Nothing has worked. I believe the problem may be that when we purchased Minecraft years ago, it had nothing to do with the Microsoft Store. That's why it isn't in there! I don't know what to do. I am going on hour 5 here. This is ridiculous.