why my wifi adapter TL-WN722N can t reach speeds of 100 mbps?

your problem is more likely a weak wireless signal; wireless radio signals (and wireless networks are wireless radio signals) weaken with distance and even more when they are expected to penetrate building materials like walls, etc. A weak signal has numerous dropped packets giving you the slower speed. Measure the strength if you have the tools to do this and change position of the wireless access point or add another wireless access point

It may be your location from the router. Distance and objects in the way matter. Also the speed will drop if anyone else is sharing the wifi.

https://www.amazon.com/ASUS-Dual-Band-Super-Fast-G...

The key is that it runs ASUSWRT which is open source and gets updated frequently. It allows you to tether your phone to the USB port and share its internet connection that way. It is also a proper router. So, if you, for example, put a NAS on the router and run a PLEX server on it, you should be able to stream content from the NAS to the TV without your phone connected.

Mind you, I question any router that is under a hundred bucks as you get what you pay for.

A cell phone is not a router. You have to receive the packets, rewrite them (because it is a NAT) and send them on. WIFI is also a shared network, you have to negotiate clear air because it can't handle collisions.'

Routers optimize things, but they still use memory. 150 users is ludicrous, maybe it has the ability to handle that many connections but that must be theoretical. I run some enterprise wfi APs, and we try and get < 15 users per AP for office area. A conference, we can handle 100 per AP. But that isn't full throttle, like streaming video. Probably web browsing/mail service at most.

cuz u need throw it out and buy mikrotik or cisco

depends on many things. it might be a fault on your phone's part. get a WiFi adapter that supports 5GHz WiFi and tether 5GHz WiFi from your phone afterwards. the difference will be night and day

Might depend on your Modem/Router as well

The mbps mentioned on network adapters is internet sharing speed, it doesn't determine internet speed.