how to enable monitor mode in windows 11

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Please guide me to how I can enable monitor mode and capture eapol and http packets.

I guess you should start with obtaining an adapter that supports monitor mode on your chosen platform? Google shows npcap, the capture library for Windows that is typically used, has a webpage with options: https://secwiki.org/w/Npcap/WiFi_adapters

Can someone please explain the reason?

The reason is that even though there is some capability within npcap and Windows to support monitor mode, it is very limited. HW options are limited; sometimes you can get some 802.11 frames but can't change channels; sometimes only low modulated (e.g. 802.11b/g) frames are picked up (which is a likely problem if you want http packets). Most times, the radiotap header does not contain useful metadata like RSSI, datarate, etc. All in all, Windows with npcap is a poor solution for wifi capture and it is not suitable for professional use (this is an opinion of course).

If, however, none of these limitations are important to you, then purchase a supported adapter and see if it meets your needs. It is still a valuable learning experience.