Yes, it’s normal. But the mismatched RAM setup isn’t ideal.
Match Your RAM for the Best Performance
… if your first stick is 4GB, you can still add a new 8GB stick. Once you switch on dual-channel mode (also called flex mode), it will perform as two 4GB sticks running side by side …
The remaining 4GB of the new stick will run in single-channel mode. Overall, it’s not as fast as using two sticks of the same size. . .
It’s the same with frequency or speed. Your RAM sticks will work together at the frequency of the lower stick by default.
Read more: https://www.makeuseof.com/tag/myths-misconceptions-about-ram/
Does it work? Yes. But is it the best? No.