Downloading Tahoe from the App Store

You cannot do it through app store any more, but per apple support, you can do download it vi terminal,
You can use Terminal to download the installer for compatible macOS versions no earlier than the version that came with your Mac, or the closest version still available.
Make sure that your Mac is using macOS Catalina 10.15 or later.
Open Terminal, which is in the Utilities folder of the Applications folder. Or use Spotlight in the menu bar to find and open it.
Type the following command in Terminal, replacing <number> with the latest macOS version number for the compatible macOS that you want to download: softwareupdate --fetch-full-installer --full-installer-version <number>
Example: softwareupdate --fetch-full-installer --full-installer-version 26.0.1
Example: softwareupdate --fetch-full-installer --full-installer-version 15.7.1
Press Return to enter the command. As macOS downloads to the Applications folder, Terminal shows the percentage installed (downloaded). If Terminal says update not found, that version of macOS is not available for your Mac. You can enter softwareupdate --list-full-installers to get a list of macOS versions that are currently available for your Mac.
Open the Applications folder and double-click the macOS installer, named Install [Version Name], then follow the onscreen installation instructions. Or leave the installer in the Applications folder for later use.

https://support.apple.com/en-us/102662