The laptop I want to buy has Ryzen 5 4500u AMD Radeon graphics, 16 GB RAM 2400 MHz.
RAM memory speed slows down CPU after all, or am I wrong? Can you overclock RAM without any problems? Never did that before. If so, how much MHz would I have?
No, you definitely won't be able to. Most notebooks lack the options in the bios!
Notebooks have a lousy cooling concept and do not have the capacity to compensate for the increased heat development through overclocking.
The speed of the memory does not have a great impact on the overall performance of the system. The effective 5-10% that could be achieved with good overclocking makes no noticeable difference.
Since, according to the description, the device will only come with an APU anyway and presumably does not have a dedicated graphics card, the RAM is certainly not a bottleneck.