I think InDesign assumes that you want to make a design system, and in that way is different in how other applications have done the gradient tool. Building a style guide you will for colours use Swatches which are in effect "Colour Styles", though they are not called that. The idea is you drag from your working palette of colours (in your swatches) to your gradient panel. (yes if you are used to Illsutrator where you can click on the gradient you are dissapointed)
An alternative way is to create a gradient swatch… then once you edit a Gradient Swatch you will see that you can add colour stops from any colour model as well as change their, Swatch, RGB, CMYK, LAB, Spot colour… (Unlike Illustrator or Photoshop there is not the option to define transparency on a colour stop, but there is a special type of gradient called the gradient feather.) I understand that you may be frustrated by these limitations if you are expecting the flexibility of Photoshop or Illustrator gradients. I hope this helps you manage what you have. If you want to formulate what you want there is a User Voice or Feature request that you can share your comments on https://indesign.uservoice.com/forums/601021-adobe-indesign-feature-requests/suggestions/36080107-indesign-gradient-tool
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