40% through tech stocks?

Is it realistic to make a return of 40% in 1 year with 5-6 different American Silicon Valley companies? (Tesla, Apple, Netflix, Microsoft, Paypal etc.)

No.

With Apple, it worked for me in the past. You can't know what the future will bring.

In principle, 40% is quite possible with individual shares. Not just in the tech sector. But you can never know that beforehand. Therefore it is better to spread the word broader than to be too specialized. Better on average only 6% p.a. Than being too greedy and losing 50% in the end