How difficult is it to branch transfer from Navy to Army halfway through one's contract?

Before mid-2022, you could apply for an early separation through your command, but according to the Navy's HR website*, they have canceled all early separations (per NAVADMIN 142/22*) except for:
● Applications to transfer to United States Space Force (USSF)
● Pursuit of a commission in the Navy
● Applications to transfer to other Uniformed Service at SEAOS

I'm not fluent in 'squid', but I believe SEAOS is pretty much the same as ETS in the Army (when your enlistment contract is up), so ... what MSG (Join to see) said.
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* https://www.mynavyhr.navy.mil/Career-Management/Personnel-Conduct-Sep/Enlisted-Separations/
* https://www.mynavyhr.navy.mil/Portals/55/Messages/NAVADMIN/NAV2022/NAV22142.txt

You will have to EAS/ETS, and then you can join the Army.

PO3 (Join to see) Two strong negatives don't add up to a healthy career positive. What attracted you to your branch and specialty? Identify and revisit the reasons to see if you can recapture that outlook. You might also consider an application to cross train into another specialty within the branch. Not sure what your options are, but since you are probably locked in for your contract's duration, you need to find a way to (survive is the best word I can think of) to your ETS.