I was faced with the same no wifi problem with a new Lenovo Legion 5 Plus. A series of posts by @moson was a great help to me in fixing it.
Here’s the procedure that worked for me:
With Ethernet connected, start pamac, the utility to install software, search for these packages (they will all be in AUR):
linux512-headers
linux-firmware
rtw89-dkms-git
They should all be there. Install each of them in sequence (you might be able to check them all and apply the install at once, but I did each install individually in sequence)
Following the installs, do a full shutdown; boot (with Ethernet still attached); you should now see both the wired and wireless up and running; disconnect the Ethernet to test the wireless; the wireless should be working (you will, of course, have to log in to your router with your wireless password)!
Hope that helps.