You would need a new laptop if your current one is determined by Microsoft to not be able to run Windows 11.

Windows 10 will be supported into 2025, so you do not need to worry for now.

I would recommend waiting a few months until the next round of CPU updates are available. While you could purchase a motherboard, CPU, and memory now that will run Windows 11, Intel's Alder Lake (12 generation) CPUs will better support Windows 11 capabilities, and motherboards for these CPUs will have support for faster memory and other speed improvements. If you are thinking of using an AMD CPU, let us know and we will see what we can find out about upcoming AMD CPU releases.

Newegg has motherboards, CPUs, memory, and anything else you might need. Amazon also has these items.
https://www.newegg.com/
https://www.amazon.com/