Speed 941 Mbps to 20 mbps

Since my main router is having issues, I stated using my old router for time being. Specs are as below.
|Model|Xiaomi MiWiFi Mini|
|Architecture|MediaTek MT7620A ver:2 eco:6|
|Target Platform|ramips/mt7620|
|Firmware Version|OpenWrt 22.03.5 r20134-5f15225c1e / LuCI openwrt-22.03 branch git-23.093.57104-ce20b4a|
|Kernel Version|5.10.176|

On wired Lan- direct on modem I get speed of 941 mbps. when using wireless I get speed of 20mbps.

Can you guess what could be reason ?

Nope... wireless is usually slower and is subject to environmental factors, so there are possible reasons there, but we cannot guess without more details.

Also worth noting... this device appears to have a 100Mbps switch built-in, which would suggest a maximum wired connection through that device of ~94Mbps, not 940Mbps. So immediately, you can see that your device is not even remotely capable of gigabit performance in general.

Let's see your configuration.

Please copy the output of the following commands and post it here using the "Preformatted text </> " button:
Remember to redact passwords, MAC addresses and any public IP addresses you may have:

cat /etc/config/network
cat /etc/config/wireless
cat /etc/config/dhcp
cat /etc/config/firewall