short answer: no, not really

long answer, here’s an analogy that might help:

you go to https://yourbank.com/ and log in with your username and password. you click the button to go to Online Bill Pay, and tell it to send ACME Plumbing $150 because they just fixed a leak under your sink.

when you press “Send”, your browser does something like send a POST request to https://yourbank.com/send-bill-payment with a JSON blob like {"account_id": 1234567890, "recipient": "ACME Plumbing", "amount": 150.0} (this is heavily oversimplified, no actual online bank would work like this, but it’s close enough for the analogy)

and all that happens over TLS. which means it’s “secure”. but security is not an absolute, things can only be secure with a particular threat model in mind. in the case of TLS, it means that if you were doing this at a coffee shop with an open wifi connection, no one else on the coffeeshop’s wifi would be able to eavesdrop and learn your password.

(if your threat model is instead “someone at the coffeeshop looking over your shoulder while you type in your password”, no amount of TLS will save you from that)

but with the type of vulnerability Jellyfin has, someone else can simply send their own POST request to https://yourbank.com/send-bill-payment with {"account_id": 1234567890, "recipient": "Bob's Shady Plumbing", "amount": 10000.0}. and your bank account will process that as you sending $10k to Bob’s Shady Plumbing.

that request is also over TLS, but that doesn’t matter, because that’s security for a different level of the stack. the vulnerability is that you are logged in as account 1234567890, so you should be allowed to send those bill payment requests. random people who aren’t logged in as you should not be able to send bill payments on behalf of account 1234567890.