HTC is going out on a limb with the U12+, which starts at $800 and won't be sold through carriers. You would expect to get all the bells and whistles when you spend that much on a phone, but HTC is cheaping out on the accessories. This phone lacks a headphone jack as so many others do lately. However, the U12+ won't come with an adapter for your 3.5mm headphones, either.
Wow! We'd like to thank you and congratulate you in advance for your upcoming HTC U12+, Aaroni. However, it does not come with a headphone adapter. It includes, HTC Rapid Charger 3.0 with USB Type-C Cable, HTC Clear Case, & HTC USonic™ Adaptive Earphones. Thank you :)
— HTC USA (@HTCUSA) May 26, 2018
According to HTC's Twitter account, the phone comes with a charger, clear case, and USonic Type-C headphones. So, you can listen to audio using the stock headphones out of the box, but those aren't great quality. You probably have nicer 3.5mm audio devices you'd prefer to use, anyway.
Most of its past phones have included an adapter at the least. A few have had the adapter and headphones. If given a choice between the two, I think most buyers would opt for the adapter instead. The U11 had the adapter and headphones, but the cheaper U11 Life dropped the adapter. The U12+ shouldn't have the same accessory loadout as a budget phone.
Apparently, this is only an issue in certain markets like the US. In Europe, HTC is including the adapter with pre-orders. In the US, you can't get one direct from HTC at all—it's sold out. Trying to find a third-party adapter that works correctly will no doubt be soul-crushing. Type-C audio is still a complete mess, which is why OEMs really, really need to include the adapter. Come on, HTC.