It all depends on the difference between the two RAM sticks: If one is a DDR4 stick and the other is a different DDR3 stick, then no, the two sticks are not compatible because the motherboard is only compatible with one of the two formats. If one is a DDR4 3000 Mhz stick and the other is a DDR4 3300 Mhz stick, then yes, these two sticks can be installed together on the same computer.
However, it's important to note that the system will use the same speed for both sticks, which will be 3000 Mhz, the lower of the two. That's why it's not recommended to mix sticks of different frequencies as it represents a waste of resources. Lastly, if one stick is a DIMM stick and the other is a SO-DIMM stick, these sticks are only compatible with desktop PCs for the former and laptops for the latter, so they cannot be used together.