Problems connecting Apple Wireless Keyboard (Aluminum) to MacBook

I have an old Apple Wireless Keyboard (model A1314) that has served me very well. Yesterday it suddenly stopped connecting to my MacBook Pro (M1). It was listed, but clicking on connect did nothing. I made macOS Ventura forget the device and tried to reconnect it, but to no avail. I shut down the keyboard and rebooted everything, still no luck. I held the power button on the keyboard (no cable to connect with) until it flashed, tried several new batteries, asked the internet and just could not find a solution.

It turned out that I had to press and hold the power button on my keyboard until it went into pairing mode, and I had to hold it down throughout the entire setup process, even while entering the pairing code (it did not even show up with my other approaches, only spinning indicators resulting in dead ends). I am 100% certain that I have never performed such an acrobatic dance to connect a keyboard to a computer before. But maybe I'm going senile.