Keyboard shortcuts
Pick the shortcuts your hands already know. They work while the remote desktop has focus (click it first); typing in the connection form never triggers them.
Keys the browser keeps
Some combinations never reach a web page: the operating system takes them first. Ctrl + Alt + Delete on Windows is one, which is why the mstsc profile sends it as Ctrl + Alt + End. Ctrl + W, Ctrl + T and Alt + Tab belong to the browser while the page is in a window.
In full screen the page asks for Keyboard Lock (Chrome and Edge), and then Esc and the Windows key go to the remote desktop too. To leave full screen, hold Esc, or use the toolbar at the top of the screen: move the pointer to the top edge to show it, and pin it with 📌 to keep it there.
Full screen and Disconnect are on the toolbar as well, so neither depends on a key the browser may keep.