Delta data point. I booked thru Capital One and waited 48 hours and tried to cancel via Delta app and website, not allowed. Contacted Delta support and they will not touch the booking as it was booked 3rd party. Had to cancel via Capital One and now have a Delta airline credit in my C1 portal. Luckily I only booked a $300 flight and I fly Delta enough I'll use it but it looks like they may be tightening up the reigns. I had no trouble cancelling directly through Delta in 2023 for ecredit. I'm sure if you put up enough of a fight you could probably win, but I'm not wasting my time over $300 that I'd use for Delta anyways. Just a bit annoying since the flexibility is not what it used to be.