Macbook could not be fully charged

It may not be abnormal. Refer to Get help with your Mac notebook battery - Apple Support:

If your Mac won't charge to 100%

If you use optimized battery charging in macOS Big Sur or later, or use macOS Catalina or earlier, occasionally the battery might not show a full charge (100%) in macOS, even after the power adapter has been connected for an extended period of time. This behavior is normal and helps prolong the overall life of the battery.

If charging is on hold and you need your Mac fully charged sooner, learn how to resume charging.

Optimized battery charging is not available in Sierra.

By comparison, the way Sierra did things was practically antiquated, but the Support document that described how it worked was removed a while ago. As I recall, your battery will charge to at least 95% and then charge at a reduced rate. It might not ever reach 100% and it's normal for it stop at (for example) 98% or 99%. If you were to then disconnect it, it would not resume charging until its state of charge fell below 95%.

But this is just from memory. Your battery seems to be working the way it's supposed to work. Definitely do not concern yourself with it, because after you use the Mac and discharge the battery somewhat it will probably recharge to 100%, or close to it. That last few percent isn't worth it because repeatedly charging to 100% will have an effect on a battery's longevity.

The 100% value is predicated on a battery's full charge capacity, which is always lower than its original design capacity. The reason for the discrepancy you are observing can be explained by the fact its latest "full charge" reflects a revised, lower capacity. That's to be expected.

Newer Macs and newer macOS versions incorporate battery management algorithms designed to maximize a battery's longevity. You can upgrade macOS on that Mac: Update macOS on Mac - Apple Support. To upgrade to an earlier version of macOS, read How to get old versions of macOS - Apple Support.