2.4 GHZ WiFi slow

I do not recommend that anyone uses 40 MHz unless they are in a very sparsely populated area.

For 2.4 GHz you should use only 3 or 4 channels. See Buffering & lagging after transition from ethernet to Wifi - #18 by JimKnopf for a discussion of which ones to choose. Don’t go for the in-between channels.