https://youtu.be/CCeq5PChvuk
It talks in detail about Catena and how they do it without keeping unnecessary UTXOS in Bitcoin as compared to 2 other companies, he says they write msgs in place of UTXO value and like burn sign with a random value of public key (no corresponding private key), while Catena signs the msgs with their public key so their TXs is like sending the same UTXO back& forth to themselves
Blockstack
https://www.investopedia.com/terms/b/blockstack.asp
https://www.coindesk.com/company/blockstack
& KeyBase
https://keybase.io/
https://techcrunch.com/2020/05/07/zoom-acquires-keybase-to-get-end-to-end-encryption-expertise/?guccounter=1&guce_referrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8&guce_referrer_sig=AQAAAMLzsAYotgrbPm8HkQVequM5OFQETe9wrlVDJsZfvmEqs3ly63a61aDqKZA3HIlPF4T9nareGqsG-lr6D56utNzJPAgALi0cEk_yfnny_lNTBvo45SFIR0hPgTaBaecdIfn4L4GsDgXdD6z2pZ2ierJwlvvORN1aK6-VzioaAZdW
https://en.m.wikipedia.org/wiki/Keybase
However, I only find rare trace of actual activities of the 3 since 2019/2020 at max, even Catena twitter is not active
https://mobile.twitter.com/catenacapital/with_replies?lang=en
.
(I didn't read the article about KeyBase being used in Zoom yet to see if it's still working and with the UTXOS use)