Fist of all : Do not panic
This wordpress error does not mean in any way that you have lost your files, your installation is intact. That’s why WordPress manages to send you this error. This means that your site is still installed on your server or on your web host’s servers .
What causes this error?
One of the main causes of this error is that you tried to access your WordPress site during the updates. Your site is therefore put in secure mode so that the update completes without any problem. Thus, a temporary home page has been created, which prevents the system from blocking permanently.
The solution: wait
In the vast majority of cases, it suffices to wait a few minutes (5 to 10 minutes), generally the time for the WordPress cache collector to activate itself. Once the cache collector have passed, this temporary home page will be deleted and you will be able to access your site normally again. Clearly in the vast majority of cases you do not have to do anything to resolve this problem.
Watch out for scams
Some websites try to sell you a service to solve this problem. Watch out for scams.