I lived in Japan as a member of the JET programme in 2021. I am now back in my home state, but was always a resident of my state. what do I put as my state of residence?

It depends on your state. 

You say you were "always a resident of my state". In most states, you remain a resident until you abandon your residency and establish a new one. Because your programme was of temporary and of limited duration, and you returned to your home state, are probably remain a resident.

Additionally, states generally say you remain a resident for a period if your absence is due to work. For example, in California you can be away for 546 days and remain a resident.

Here is one of their examples:

You are a resident of California. You accept a 15-month assignment in Saudi Arabia. You put your personal belongings, including your automobile, in storage in California. You have a California driver’s license
and are registered to vote in California. You maintain bank accounts in California. In Saudi Arabia, you stay in a compound provided for you by your employer, and the only ties you establish there are connected to your
employment. Upon completion of your assignment, you will return to California.

Determination: You have maintained greater connections with California than you have established in Saudi
Arabia. Your absence is for a temporary or transitory purpose. Therefore, you remain a California resident.
As a California resident, your income from all sources is taxable by California, including the income that you
earned from your assignment in Saudi Arabia.

Check you state specific rules.