Store gone from Apple TV+

It seems you are using the Apple TV Preview app for Windows. As that is pre-release software, some features may not work as expected. I can’t verify that.

I think the Store tab (and channels like Apple TV+, MLS) should be in-between the Search field and the Library. Unless you are offline. Or unless the sign-in account is for a country that doesn’t have Apple video services, and instead the Apple TV app only supports local media files.

If connectivity or regionality is not the issue, then alternatively you may browse the store, buy, or rent on any other supported device, and your purchase would sync through your Apple ID account.

This is a network issue. If you're "Offline" (Wifi or VPN blocking connection), the store tab will not be there. Simply close the AppleTV app. Resolve the network issue and relaunch. WaaLaa! The store reappears.