Mac pro battery maximum capacity drop

Apple never previously showed the battery capacity to users before, so most people don't realize how this value changes over time. In fact, you may even see this value fluctuate up & down (unless macOS only lists the lowest value encountered.....I haven't had the opportunity to test how macOS reports this value).

I have done a lot of testing on Intel Macs where I have pulled the raw battery information from the battery using command line utilities available with macOS. When observing the battery's Full Charge Capacity (FCC) in one minute increments I have found the FCC value tends to fluctuate even with a good battery. As the battery ages/wears these fluctuations will grow larger to the point they indicate a failing battery. Even the small fluctuations in the batteries FCC value can cause a several percentage point change in the battery's max capacity percentage. Unfortunately these same command line tools don't pull the same details from the Apple Silicon Macs' batteries....there are other macOS built-in utilities which can retrieve this information, but it is much more difficult to parse & requires a custom script or utility to pull, parse, and display the information.

Just ignore the Battery Max Capacity value unless you actually have a problem with the battery where it is not performing to your expectations. Of course you can monitor this value to learn how it works/behaves with your Mac.

Also, ignore the Battery Cycle Count as well since it is meaningless unless you are having battery issues and it is nearing 1,000 cycles where it indicates your battery is probably well worn & will be needing to be replaced soon.

It's not abnormal. Read Get help with your Mac laptop battery - Apple Support.

A battery starts with a maximum charge capacity of 100% and can only diminish. It does not diminish at anything resembling a linear rate. It may even increase from time to time. Therefore its future maximum charge capacity cannot be extrapolated to some future date.