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Thank you.

This has been dupped 4-5 times.

Your solution had been avoided early on since it might be massive bytes issues -- many exact similar huge Data URIs in many SRCSET defeating performance intentions.

The current solution about:blank is the only valid and most efficient. Please read the issue linked thoroughly for more details.

However as said is dups, feel free to offer a better solution that account for W3C validity and efficiency above. See, valid for one, not valid for other tools?

In case confused about my previous comment, your previous proposed solution may contain huge Data URI when Blur aka massive bytes is enabled, that is why avoided from the start.

Another fairly efficient is to use GIF:
https://git.drupalcode.org/project/blazy/-/blob/8.x-2.x/src/Media/Placeh...

Not blank SVG, nor your dynamic Data URI, which is still acceptable for controller image, but not massive SRCSETs.

That GIF might be in if all validators agree. You need to confirm that those tools verify it correctly.

3.x is out.

Any betterment should start here, and may or may not be backported.