If your package's dependency for Umbraco doesn't have an upper bound, the Marketplace will automatically assume your package works from the referenced version and up. So eg. if your package has

<PackageReference Include="Umbraco.Cms.Web.BackOffice" Version="10.6.1" />

, the Marketplace will show that it supports Umbraco 10, 11 and 12. This will probably also be the case for most packages, but there is a chance that the Marketplace may be wrong. For most of my packages I have something like this:

xml
<PackageReference Include="Umbraco.Cms.Core" Version="[10.0.0,12.999)" />

There are pros and cons about either way, so either way should also be fine 😉