With 2019 I'm always able to change the code, but since the debugger is not paused the change, highlighted with a green squiggle, can't be compiled on the fly.
This is the "expected behavior" since VS 2019 16.3. It was reported as a bug/regression on developercommunity.visualstudio.com under Able to type while debugging back in Oct 2019, and was resolved as "Closed - Not a Bug". Quoting from the Microsoft-sanctioned comments:
This behavior you described is expected for Visual Studio 16.3. We went through several changes on Edit and Continue and now allow editing the code while the application is running. Any errors or warnings regarding your changes will show up at the Error List Window. In order to apply these changes, you simply have to be on a break state (e.g. break all or stop on a breakpoint) and continue from there.
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The new design allows you to edit the code while running, however these changes won't be actually applied until you stop at a breakpoint or break your app, so you'll have pretty much the same behavior as before.
If you edit your code with Edit and Continue disabled, you'll be notified that the file changed (only if "Require source files to exactly match the original version" is checked), but you shouldn't be forced to restart the app.