This is probably a regression as I remember it working quite fine before. When I create a vector selection and then try to edit it, I use "Select Shapes Tool". However, clicking anywhere in the image results in a popup "This tool only works on vector layers". Double clicking inside the selection switches to "Edit Shapes Tool" which only allows to change the corner radius of the selection. Then I can switch back to "Select Shapes Tool" and see the points to resize the selection but yet again it doesn't allow me to showing the same popup about vector layers.
That's because editing selections is now part of the selection tool. Vector selections are the default now. You can still use the vector tools to edit selections by either creating a local selection and selecting or choosing show global selection mask in the selection menu and selecting that.
Ok, that's not very intuitive and I still would prefer the old method but it works (only in the nightly version it seems). I don't see the difference between "Edit selection" and "Show Global Selection Mask" though.