mTLS for offsite payment app

[Alaa]

I'm developing an app with offsite payment extension, it implements payment, capture, refund, and void session and it is working fine. It does not use mTLS , but recently I received an email says that shopify changed its certificate authority architecture and I have to add the new certificate root public key to my trust store.
the new key and the docs are here:
https://shopify.dev/docs/apps/build/payments/considerations?syclid=cqlinss0p36s73agcosg&utm_campaign...

my question:  how my app is working fine without mTLS?

[Brandweb]

Is your offsite payments app still working?
Mine is not and I also got a reply from Shopify Support that it is due to mTLS.