WritersCafe.org does that with every post. I just provide the stamp on all my shares of those works elsewhere. For example, my poem, "For the Children" includes the copyright date stamp, "© 15 April 2022" because that's the date of the same poem posted on WritersCafe.org.

Here's the poem on WritersCafe: https://www.writerscafe.org/writing/MomzillaNC/2813364/

Here's the poem on Medium: https://medium.com/illumination/for-the-children-9b14ec7b6aa9

The poem is also on WordPress here: https://momzillanc.wordpress.com/2022/04/28/for-the-children/

On WritersCafe, every post displays the platform issued copyright below each work, plus includes a platform digital record of the "date added" and "last updated" dates for every post. Having that previously posted publishing copyright date stamp is protection itself. And, the poem exists in multiple places, published in my name, with that date stamp. Because the date stamp is internal to WritersCafe.org, a plagiarizer cannot fake their own earlier publishing date stamp.

It might not be 100% safe, but, if it comes to a legal confrontation, my creative writing is 100% provable to be mine dating from any plagiarizer could claim ownership.