Can't export full size in Photoshop

The answer seems to be in the tool tip for the warning icon that appears when the number of pixels exceed a certain amount, as shown in the picture below.

Use File > Save a Copy instead, which also can save a JPEG image, and it seems to have a much higher pixel limit.

It always does this for larger prints.

By @Mark Shian LS

Because you mentioned “prints,” File > Export > Export As should not be used for that. Export As is designed for web/mobile graphics, as a replacement for the deprecated File > Export > Save for Web (Legacy) command. This misunderstanding is not your fault; the Photoshop UI does not make it obvious why it has so many different commands for creating a JPEG and which command is for which type of delivery. This has caused a great deal of confusion.

File > Save a Copy is a much better way to create a JPEG for print, because it’s sort of a “full service” export that’s free of many of the limitations in Export As and Save for Web that were put in place so that web/mobile graphics would not be too large to download. Not only does File > Save a Copy have a much higher pixel limit (I’m not sure what the limit is), but also, Save a Copy retains all metadata including the PPI resolution value. For example, you mentioned 300 ppi, but the ppi metadata is not retained by Export As or Save for Web because ppi is not used in web/mobile.