There are typically agreements with ATM operators to allow no-fee withdrawals, and you can usually do cashback at the register when making a purchase in many stores, but beyond that you’d need to find an office that can handle cash and not all credit unions have those.

Entirely depends on the CU

I know the ones in Australia would let you withdraw in person , if you were in a town with that CU or via an ATM.

I believe banks are able to pause transactions out if they approach their solvency thresholds.

I’m going to answer the last part of the question, banks and credit unions and these institutions absolutely can, will, and do limit withdrawals. When you don’t physically hold your money and it is in an institution, it is no longer your money, it is an IOU with conditions that can be rescinded at any time for any reason.

In the U.S. most credit unions are regional, if you go to a branch you can withdraw cash easily, or they’ll have agreements with ATM networks where you can withdraw cash for a fee, just like banks do.

In my daily life my credit union is indistinguishable from a bank, with the exception that I’ve had a few auto loans from my credit unions and they’ve always offered a lower interest rate than anything a bank or car dealership can beat. They also gave me a discounted rate because I was buying an electric car.