If something is new and useful there is a good chance it is patent eligible in one form or another.
35 U.S.C. 101 defines the four categories of invention that Congress deemed to be the appropriate subject matter of a patent: processes, machines, manufactures and compositions of matter.
Manual of Patent Examining Procedure 2106 (I)
The range of things that are patentable is immense. It is easier to talk about things that are not patentable. The USPTO follows limitations set out by the courts concerning what cannot be patented. The limitations lie in the general area described below:
Because abstract ideas, laws of nature, and natural phenomenon “are the basic tools of scientific and technological work”, the Supreme Court has expressed concern that monopolizing these tools by granting patent rights may impede innovation rather than promote it.
Manual of Patent Examining Procedure 2106 (I) quoting Alice Corp. Pty. Ltd. v. CLS Bank Int’l, 573 U.S. 208 at 216
The specific rules can be quite difficult to follow accurately without experience. This is an area where someone with insufficient experience could quite easily come to the wrong conclusion. For example, careful wording by a patent attorney could achieve patent protection where many would assume the rules forbid it.