Well known web site iFixIt.com has found that customers could upgrade the newest Mac mini RAM if they wish.
Here’s a sample of what the steps are:
- Power down your Mac mini, disconnect all of the cables, and flip it over.
- Use the plastic opening tool to pry the bottom cover up off of the Mac mini. It removes easily. This pic is from the 2014 model but the process is the same for the 2018 model too.
For more information, click here.