A customizable Knob block was introduced in R2021a. You can find the documentation for it here:
Also, from what I understand, you have your dashboard blocks in a panel (I assume you mean this when you refer to panels: https://www.mathworks.com/help/simulink/ug/interactively-debug-your-models-using-panels.html ), and when you zoom out, the blocks do not change size. Panels float above the model, and so the panel and its contents do not zoom with the model.
If you have only one tab in your panel, and you want to create a dashboard that acts as a part of the model rather than floating above it (i.e. a dashboard that zooms in and out with the model), then instead of having blocks in a panel, you can just have the blocks in the canvas and add a background image under them.
To add an image to the Simulink canvas, see the following documentation:
