My New Samsung phone has no ear/headphone jack. News to me.

Yep. I used the adaptor for a while. There's one that has two connectors, allowing you to connect a charger to one and your headset to another. So when you're out for a long travel day, you can still listen to museum audio guides.

And then I bought my wireless headset.

It's time to get a bluetooth adapter if you want to use wired headphones. I tried the adapters that plug into the charge port but never got them to work well.

Or switch to wireless headphones or earbuds.

I have both a set of wireless headphones and earbuds. I bought the wired ones for the overseas flight to the US. Unless Delta has gone wireless??

Im not sure I understand your question. What do you need the headphones for? For your phone? Or to use the inflight entertainment system? If the latter; doesn’t Delta provide headphones?

I bought a Samsung S24, which has no round phone jack. I was in a Dollar Tree, and bought a few wired earphones with Type C connectors. They have a little volume control and contain a microphone for making phone calls. They cost $1.25 each, and sound fine to me. So now I have one in my carryon bag. As noted, the airlines still use the round miniature plug, so I carry one or two of those also. But, airlines pass those out before takeoff anyway.

Samsung devices without a 3.5mm jack has been the reality for many years - going back to the Note 10 for me. Kind of liberating not having to have eaebuds tethered to the phone to have audio.

If you want to continue using 3.5mm earbuds get a USB C to 3.5mm Headphone Adapter, Male to Female - https://www.amazon.com/dp/B07VL9XCQ5?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

USB C earbuds are inexpensive.

Or just go with Bluetooth earbuds. I like the SoundPEATS Q30 HD+ Bluetooth Headphones, but there are so many options at several pricepoints.

Personally I have a pair of 3.5mm, USB C and a couple pairs of Bluetooth earbuds that live in my bag for whatever situation.

If the latter; doesn’t Delta provide headphones?

They do, but as you might expect the quality of those headphones is pretty low. Some years ago I bought a pair of wired earbuds with better insulation and it's made a world of difference for watching movies on planes -- I no longer have to turn up the volume all the way up to hear the movie over the noise of the engines.

(What is actually the best for me is pairing my AirPods with planes, which some United planes have and I think some Delta planes are starting to have as well, but I continue to carry my wired earbuds on all planes in case I can't get them to pair.)

Several years ago Samsung mocked Apple for removing the headphone jack and then 2 years later they removed the headphone jack.

I remember when I bought a new Samsung phone several years ago and it had no headphone jack. I bought some wireless ones, but never really adjusted to them. Maybe now that I have hearing aides I'll try to get used to the wireless earphones again as they are similar to my hearing aides when using their volume control, etc.

the airlines still use the round miniature plug

Not all airlines. Some use a 3 prong plug.

When I upgraded my Samsung phone I bought an adator that plugs into the charging jack and has a 'hers' socket into which you plug your wired headphones. Works a treat...for some things, better than my wireless earphones.

What is actually the best for me is pairing my AirPods with planes,
which some United planes have and I think some Delta planes are
starting to have as well, but I continue to carry my wired earbuds on
all planes in case I can't get them to pair.

The last two international Delta flights I was on in the past two weeks still required wired headphones. I don't know if an airfly adapter would work and didn't notice anyone using one (like this https://a.co/d/16uas8l).

FWIW, this is a link to the specific adapter I got for my old Samsung, and now Pixel, phones. You can charge and listen at same time. Works just fine. https://a.co/d/1yK2sLm