Photoshop 21 on widows 7

Officially Adobe only supports up to photoshop 2020 on windows 7.

https://helpx.adobe.com/photoshop/system-requirements/earlier-versions.html

I guess it depends on whether you meant photoshop 2021(photoshop version 22) or photoshop version 21 which is photoshop 2020.

Another issue i've found is that when installing a 64 bit version of photoshop cc not officially supported by the current version plus one back policy, that no updates (bug fixes) are made availble for the older unsupported photoshop version such photoshop 2020. In contrast if one installs a 32 bit version like 2018, then Adobe does offer updates.