1366 Incorrect string value: '\xF0\x9F\x98\xA2\x..

Hi,
I am using the template tp_hope for building up a new website for my wife. Very sporadically I am getting error message in frontend as well as in backend:
1366 Incorrect string value: '\xF0\x9F\x98\xA2\x0D\x0A...' for column 'body' at row 1
This is curious because error appears only from time to time and refreshing the browser two times shows the expected content.Website is currently offline but it could even appear that error message comes before you see the logon screen. In summary it is hard to reproduce the error.
Unfortunately we strongly enhanced and changed the system (content, modules, etc.) over the last weekend means I am not able to detect the cause.
Here are some details:
Joomla! 4.0.6
MySQL 5.7
PHP 7.4
I found some postings saying that error message has something to do with UTF8 encoding. But MySQL database has collation utf8_general_ci what should be correct.

Who could help me ? Appreciate your help.
Regards,
Carsten

Hello, live Url please.
And what is installed as well instead of theme and astroid?

Hi,
thank you. This is solved meanwhile. Found out that a plugin for sending out newsletter caused the error messages. After changing corresponding tables to utf8mb4_general_ci it works.
Regards,
Carsten