I have the same problem as described here:

https://community.tp-link.com/en/home/forum/topic/655042

I use TP-LINK Archer MR200 branded by Orange (out of warranty already). I want to use it in "Wireless Access Point Mode" - I'm not using SIM card to connect to Internet. Instead, I only want to use the router as a switch (repeater) with Wi-Fi hot spot. Everything works, however, upload speed is unbelievably slow. Does not matter, if I'm connected over Wi-Fi or over Ethernet cable. Upload speed is about 0.001 Mbps.

Not sure why you replied to thread above with private message, however, if the advice is secret somehow, can you share the secret how to fix this?

I also tried to download the latest firmware from here:

https://www.tp-link.com/cz/support/download/archer-mr200/v4/#Firmware

I downloaded the one dated 2021-03-08 , but when I tried to apply it to the router, then after a while I received an error message stating, that the file is not applicable to my router (I unzipped and tried to apply the "bin" file, of course).

Thank you.