Which of the two laptops has the better cpu?

Can the ram be upgraded for both?

which of the two is generally better (apart from the ram)

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The Ryzen 7 5800H is better. So the second laptop.

And how much mHz can the ram have? So how much is best?

The second has the better cpu, but is also 1/2 KG heavier.

In general, 17 inch laptops are rather questionable, as they are often too big for mobile use and you still need a stationary monitor.