Macro warning shows despite no macros contained in document

I have a document which I created long ago and for quite some time, every time I open it I get the infamous Macro Security Warning (“This document contains macros.”).
Problem being that I never added macros to the document. With some searching I found this similar topic but their solution doesn’t work for me. If I open Tools -> Macros -> Organize Macros -> LibreOffice Basic I only see the Standard library but nothing else which is deletable.
Any ideas?

You do not need to have any macros in document to get the warning.
I understand you have stated that you have never added macros in a document. Regardless, and just to make sure you check this also, even if there are no macros currently present in the document, if there is an event with a link to a macro (once there and now code is gone) you will get the warning. Example event:

Should also note this may be because of a python macro not in the document but referred to in an event.
Another item to check may be something installed in Extension Manager.

To analyse: Copy the file and delete the text in this copy. Save and re-open. Macro-warning still there? Then upload this copy here, so one can look for events, python, java-script… as you wrote you only checked Basic.
To clean without knowing the cause?
Create a new empty file and copy all contents of you old file to the new one. Save and re-open. It macro-warning is now “copied” to the new file try again with smaller parts of the document like first half/second part to find the place.

This warning would also appear when you have a module in your document (even empty). I don’t know how it could appear in a document for which you never created macros, but anyway: you might want to open Basic IDE (Tools|Macros|Edit Macros), and check Tools|Select Module|Modules tab, expand your document node, and remove all modules you see there.

The OpenOffice default template I used to use several years included 21 empty event declarations. All documents derived from that template raise a macro warning in recent versions of LibreOffice although nothing points to any macro.
Sample file: and hundreds more attachments on having a content.xml starting like this:

<office:document-content office:version="1.2">
        <script:event-listener script:language="ooo:script" script:event-name="office:start-app"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:close-app"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:new"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:load-finished"/>
        <script:event-listener script:language="ooo:script" script:event-name="dom:load"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:prepare-unload"/>
        <script:event-listener script:language="ooo:script" script:event-name="dom:unload"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:save"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:save-done"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:save-as"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:save-as-done"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:copy-to"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:copy-to-done"/>
        <script:event-listener script:language="ooo:script" script:event-name="dom:DOMFocusIn"/>
        <script:event-listener script:language="ooo:script" script:event-name="dom:DOMFocusOut"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:print"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:view-created"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:prepare-view-closing"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:view-close"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:modify-changed"/>
        <script:event-listener script:language="ooo:script" script:event-name="office:visarea-changed"/>

This appeared in 6.4, and was backported to 6.3.1 and 6.2.7: core commit b3edf85e explicitly enabled this new behavior. You likely would want to file an enhancement request to have some means to fix the problem, which looks absent now.

Filed tdf#152266

Thank you all for your replies.

In the end it was dead simple, in the text of my letter was some formatted piece of text which looks for me like some kind of trigger for a macro. I replaced it with plain text and the warning is gone.
Thanks for that basic tech support again, I was just so confused because I couldn’t see any macros in the Macro Organizer (not sure if the popup is called that way).