Plone 5.2: How to avoid magic transformation to relative address?

I want to embed an audio.
TinyMCE "insert media" dialog has a text field for the source address.
If I insert an absolute address of a file uploaded in this folderish page, the address is modified.
The address is modified to a relative address 'filename' as it is an object in this page.
This is unwanted as it breaks the (by TinyMCE) generated embed code, which is
…<source src="…
This is obviously wrong.

As the magic transformation is not done anymore and the problem is fixed in Plone 6.0, where can I find the code to be backported to Plone 5.2. Or where can I find a fix for Plone 5.2 for a single project?

A nice and OKish transformation would be to resolveuid:

which generates an embed code rendering lovely :heart_eyes:

and it's just audio…

For the records
Plone 6.0 is not touching the internal media url at all:

maybe this and this: