>"But it is recommended to update your processor for better support."
There is no way you can update CPU in old device with 4th Gen CPU to support Windows 11. Sockets and chip sets aren't compatible with Windows 11 supported CPU's.
Beside just like this CPU (i7-4500U) many CPU's used in laptops has FCBGAxxx (BGA = Ball Grid Array) socket which are soldered directly to mother board --> no way to update.
>"My understanding is that Windows11 currently supports most Intel Core i3 and i5 processors."
It's not depend on iX number but key thing is generation. All i3 or i5 must be gen 8 or later but
there is also few gen 7 i7 CPU's which are also supported.
>"For some reason, only a small number of Intel Core i7 processors are supported."
Some statistics from supported CPU's list:
i3: 50 supported CPU's
i5: 91 supported CPU's
i7: 76 supported CPU's
i9: 43 supported CPU's