Is it possible to add a dynamic link in the main navigation in a child theme

My client would like to have a link to the most recent post in the main navigation, but still be able to manage the navigation through the dashboard as usual. I did not find a plugin that will do this task, so I may need to custom code it. I could add it into the child theme, but I don’t think it would should up in the dashboard menu where they could move it to a different order, if they want.

TinyMCE plugin won’t work with jQuery 3.5.1 (testing with “Test jQuery Updates”)

since WordPress seems to be moving towards a long due jQuery update, I began testing a few of my plugins (they’re not published, just stuff I use for a few clients’ websites) with the “Test jQuery Updates”. Everything went smoothly until yesterday, when I ran into the following issue. I have this simple plugin that adds a few buttons to TinyMCE (yes, the theme I made for that client uses Classic Editor) for them to easily add shortcodes and pre-composed HTML snippets to their posts and pages. The code is pretty standard: first the buttons are registered via a function hooked to the ‘mce_buttons’ filter hook, then the scripts with the jQuery code for the buttons are loaded via another function hooked to ‘mce_external_plugins’. When I run this with the default WP 5.5 jQuery the button shows up in TinyMCE, while if I activate jQuery 3.5.1 (both with and without jQuery migrate), nothing appears and the worse part is that I don’t get any errors or warnings in the browser console, so I don’t have the faintest idea about what went wrong.

How to create a field in customize and show that in header.php?

I am new to WordPress coding and learning this from stackexchange,
I am trying to create one WordPress website from scratch, in header I want to show contact information for example phone number,
I want to create a field in customize and want to display the value in header.php.
Is there any guide or tutorial for that? Any help will be appreciated. Thanks a lot!!
*don’t want to use plugin