How to use?

1. Open an blend file you already have and would like to use the node in.
2. File > append > viewport-selector-node.blend > NodeTree > ViewportSelectorInt / ViewportSelectorFloat
3. Go to your geometry node editor.
4. Add a new node and search for "ViewportSelector".
5. Plugin 2 values first for viewport and second for render (or just put them by hand).
6. Use the output anywhere you want in your node tree.

Step by step video