Are you sure about that? Have you talked to a good lawyer about it?

This is not necessarily only a legal issue it's also an information security issue.

You can't guarantee the integrity and privacy of the full request and response chain.

This goes against various security standards and ISOs.

You might be able to get away with it and trust the CDN but that's an awful lot of trust.

Unless you are terminating TLS entirely on owned hardware, you are paying a 3rd party to manage TLS for you.

A lot of people seem to think that there is a big difference between paying a lessor (e.g. Hetzner) for a server on which you terminate TLS, paying a cloud host (e.g. Amazon) to terminate TLS, and paying a CDN (e.g. Fastly) to terminate TLS. Legally there is no difference aside from the specific language of the contracts, which you can review and negotiate in advance.

The difference security-wise is entirely down to the operations of each company, which again you can review and discuss in advance. Strictly speaking a CDN should have lower risk than a host since they are not persisting sensitive data (if you set your cache headers correctly). And as discussed above, using one domain helps avoids cross-domain security concerns.

You're putting a lot of trust in your CDN, anyway. If your CDN gets hacked, what's stopping your frontend code from being updated to send your API requests somewhere else? Maybe they get rerouted to a proxy, then back to you...