For me this comes out of the blue, and I expected Clickup as I read somewhere to have a business model that earns on the storage feature, not by capping essential features.
The whole reason why I like Clickup is that it gives uses the ability to really move their life and work into the platform, like Google has done because it provides the basics.
The probblem with custom fields, is that an organization or team will always create custom fields and therefore users will always go beyond 100 uses.
The whole promise and idea of unlimited users and projects makes absolutely no sense if there is a limitation in the structure of the projects, that is, the customn fields of tasks.
The result is, that I will never recommend anyone any more to use Clickup because one will be forced to to upgrade, or one has to leave the team if the team uses custom fields.
Custom fields are the most fundamental workings of the platform and therefore in my view should be part of the free accounts, otherwise promising unlimited users and projects makes no sense.