There is a lot of people jumping on here, despite us asking you not to (it’s even in our Forum Welcome and Support Guidlines that you please create your own topics, as an issue is rarely the same, especially in this case I can tell you it won’t be the same).
Now then, to the answer at hand;
WordPress 5.2 introduces new protection for sites crashing due to bad or invalid code (also known as a White Screen of Death, or WSOD for short).
If your site crashes, the message above is shown, and an email is sent to the site admin with a way to log in and deactivate the plugin or theme causing problems, once that is done the site should start working again as expected.
If you are not receiving the email, you’ll have to do the manual tasks as recommended in the usual troubleshooting guide (see the section on disabling plugins in our WordPress 5.2 Master List), in some cases, if you have access to error logs, they will show what caused the error, but in that case, make your own topic, we can’t answer all of you in this massive thread.
Because this thread is now so convoluted, I’m closing it, I encourage you to make your own topics if the above steps do not work for you, or you need help explaining them in detail.