Is reimbursement for expenses per diem meals or travel expense?

I would enter it under meals. 

For 2022, the Per Diem is considered as 'from a restaurant'.

"Is it meals or travel expense?"

For clarity, it is also referred to as "M&IE" = Meals and incidental expenses. Not travel. Travel is, for instance, train, bus, airfare. It's M&IE while traveling.

https://www.atbs.com/post/seizing-the-per-diem-tax-break

1. Your duties require you to be away from the general area of your tax home substantially longer than an ordinary day's work, AND

2. You need to sleep or rest to meet the demands of your work while away from home.

It further states that taking a nap does not satisfy the requirement. However, “you do not need to be away from home for a whole day, as long as your relief from duty is long enough to get necessary sleep or rest.”

What does this mean to a driver? If you are an owner-operator, the rule is simple, you get to claim the tax deduction for each day that you are away from your “tax home”. On the days that you depart and the days that you arrive at home, you must claim a partial day allowance instead of a full day allowance. That is ¾ of the standard allowance.

The current rate for 2023 (last updated October 1, 2021) is $69 per full day and $51.75 per partial day in the Continental US. You may hear the amount of the deduction quoted as $55.20 per full day. Temporarily for 2021 and 2022, the Taxpayer Certainty and Disaster Relief Act of 2020, allowed a 100% deduction on Per Diem. Starting in 2023, the deduction has gone back to 80%."

Oh, wait a sec, here..."Reimbursement?"

An employee truck driver doesn't get to include any allowance deduction for this on their tax return. And as long as their employer reimbursed them per the regulations, it is not taxable pay. But the employer's taxes will report that deduction.

The deduction for per diem is for the business. A self-employed (owner-operator) trucker is their own business.