I cannot enable the utf8mb4_general_ci in Control Panel Paths & Database if I do nothing works..
It was a very long time since I optimized the database 😱
Maybe it is a cookie /cache issue.
I test posted your site and it accepts 4byte unicode emojies now.
We posted on top of each other
when in the re builders screen and you click on utf8mb4 there is no progress bar ,you just need to wait till you get a confirmation screen.
It is a large screen with a lot of scrolling.
To get to the bottom with the clickable links.
If you get a error or no confirmation maybe you need to nudge your php script time up a bit.
Like from 60seconds to 120
I had to do that on my second site which is a slightly large forum
But I would change it back to default afterwards.