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The main.php file does not exist in Joomla 4. The documentation page you are reading is for Joomla 3 and marked as such at the top of the page. The correct documentation page for Admin Tools 7 for Joomla 4 is https://www.akeeba.com/documentation/admin-tools-joomla/atwafissues.html

Regarding the secret word, I think you have used characters outside the recommended range of only lowercase and uppercase ASCII characters and numbers (a-z, A-Z, 0-9), dashes and underscores in order to ensure the widest compatibility with all possible browser and server combinations. Please read https://www.akeeba.com/documentation/admin-tools-joomla/web-application-firewall.html#waf-configure-basic-protection under “Administrator secret URL parameter”. Remember what it reads:

Any other characters you use (such as: punctuation; special characters; Latin letters with accents or diacritics; Greek, Cyrillic, Chinese, Japanese and other ethnic script characters)will have to be URL-encoded. This makes it difficult and tricky to use, hence our recommendation not to use it.

> as plugins/system/admintools/admintools/main.php still exists on my server I thought it was the good way.

It shouldn't. It looks like Joomla failed to do a full update.

Please delete the entire plugins/system/admintools folder, then install the Admin Tools 7 package twice in a row, without uninstalling it before or in between.

> I think my error was to set 'Allow administrator access only to IPs in Exclusive Allow IP List' to yes.

Don't enable this option unless you have a static IP address on your Internet connection and you only ever want to access your site from that IP address. Please do read the documentation, we do explain the concept of each option in there.