When you attempt to press the "Update General Settings" button, review the page and see what the form error says. In a modern browser that supports html5 such as Chrome or Firefox, the error will display itself by highlighting the form field in red.
Correct your error, then you should be able to submit the page.
The problem is, I'm not seeing any errors. When I click on the button, nothing happens. This happens in both Safari Version 13.0.5 (15608.5.11) and Chrome Version 80.0.3987.132 (Official Build) (64-bit). I even have the Developer Toolbar enabled in Safari and Developer Mode enabled in Chrome.
I tried two things. I tried to disable the post likes box by unchecking it, and I tried to change the number of people listed in the likes from 6 to 10. In both cases, nothing happened. When I left the page and then returned, the settings had not been altered.
When I mouse over the button, the pointer changes to a hand, as it does when you mouse over a link, but when I click on the button, there is no visual change indicating that the button has been clicked on, and there is no indication of the page reloading.
Essentially, the entire General section is "dead". Neither changing box selections (from checked to unchecked) nor text settings are changed when clicking on that button.
I cannot replicate an error with the General Settings page submitting values on any of the v7.7.4 sites that I have access to.
Please attempt to submit the page then expand all of the sections on that page and look for an HTML5 error on that page; the page will not allow you to submit a page with an invalid value as of the v7.7.x series. Be sure that you expand _ALL_ sections on that page as any number of them could have the invalid value.
Example of errors attached; they will be subtle, but the page is not allowing you to submit because something on the page has an invalid value.
Well, that was weird. I expanded all the sections, made a change, clicked on the button, and the page went to the General Settings section. Under Contact Link Type, there was a popup with the words "Enter URL". The radio button labeled Forum Email Address was selected. The next line says Contact URL. That box had the email address in it. That was what was causing the error. Once I removed the email address, the error went away and the page saved as expected.
The strange thing is, I would assume that the email address has been there all along. It simply didn't generate an error until you switched the form to html5. Lesson learned.
if you do want to have separate email addresses for email that originates from your forum, and for your visitors to contact you directly at, you can do this by preceding your contact email address with "mailto:"