Good job discovering that utility & option, did you by chance get that from one of posts a while back (it certainly looks like what I may have suggested)? You will want to monitor this until it reaches 100% charge. Look for any larger FCC fluctuations over 400+ mAh.
Then keep this utility running & stress the laptop so the battery drains as quickly as possible as a quick drain will more likely show larger FCC fluctuations indicating a failing battery. Many times you can see large fluctuations at any charge level, but the best place & time to find them is when the battery is at lower charge levels. "mprime" (aka Prime95) makes it very easy to drain the battery quickly by using its "Torture Test" mode (most Intel Macs don't last more than 2 hours even on a brand new battery). If you open another Terminal window and run:
caffeinate -diu
it will prevent the laptop from sleeping including Display Sleep. Just make sure to terminate this command once you begin to charge the battery or finish with your tests. You can also just invoke "caffeinate" with "mprime" in order to start both actions together and have "caffeinate" terminate automatically once "mprime" is terminated.
caffeinate -w <path-to-mprime>
FYI, unfortunately this trick of monitoring the "pmset" output here only work with Intel Macs since Apple broke it on the M-series Macs.
If the Battery Condition shows "Service Recommended" and you are having this issue, then it means you should have the battery replaced. Ignore the "Service Recommended" condition otherwise until the battery is not performing to your expectations.
Also, keep in mind the battery charge level shown on the macOS login screen is not always showing the correct information (it may have gotten a bit better with Sonoma, but I think there are still issues). You must be completely logged into macOS to get the actual charge level (perhaps waiting a couple of minutes is advisable as well).
It would not surprise me that the battery on a 2018 laptop would be failing. I find most Lithium Batteries usually need to be replaced between 3 - 5 years.
