Is there an equivalent to Premiere's tilde key in DaVinci Resolve?
You can't expand any panel to full screen in Resolve 16 like you can in Premiere Pro.  You can expand the viewer to full screen with cmd/ctrl-F, and on the color page you can also get different viewer expansions with alt/opt-F and shift-F.
Beyond that, if a panel can be hidden, it's listed under the Workspace menu-&gt;Panels in Workspace, or by simply dimming its tab across the top of the screen. Not all panels can be hidden in Resolve.  In general, Resolve's UI is less customizable than Premiere.
BlackMagic's approach to UI design is very structured, and while it takes a period of adjustment for new users to become comfortable, it mitigates the need to hunt for shifting UI elements. &quot;Where did I put that panel&quot; doesn't happen.  Neither does &quot;Where did I get Dave's Fave Layout&quot; when your name is not Dave, but Dave shared a project with you.

You can save layout presets, under the Workspace-&gt;Layout Presets menu, and you can re-map keybindings to most commands in Resolve.  This, coupled with the fact that the positions of UI elements are consistently and predictably located make it possible to automate repetitive tasks easily with third-party macro software (e.g. autohotkey for Windows; Keyboard Maestro for Mac) which use mouse clicks in addition to keystrokes.
But DaVinci Resolve's secret killer feature is actually not one you'll find in its (oversized) manual.  It's BlackMagic's stellar support staff and developers.  If you have a reasonable feature suggestion or bug report, post it to their user forums.  They will evaluate it, and if it's a good idea, they will implement it, quickly.  The last issue I brought up wasn't even really something I considered a big deal, and there was already a workaround, but they fixed it in less than a month.  And they've implemented my suggestions on multiple occasions.
Something like the tilde key for full-screen windows has probably been brought up before, but if they see more demand than pushback for it, and as long as the feature doesn't infringe on another company's intellectual property, they'll do it.