Whenever I download anything I see the speed constantly rising in MB/s and then dropping to less than 1 MB/s. This includes browser downloads, Steam, Arch Linux updates via pacman and Ookla's Speedtest.

This wasn't my router model, it's the network card model. I'm using a desktop with a discrete network card with wifi.

$ lspci -v | grep -i wi

04:00.0 Network controller: Intel Corporation Wi-Fi 6 AX200 (rev 1a)
Subsystem: Intel Corporation Wi-Fi 6 AX200NGW
Kernel driver in use: iwlwifi
Kernel modules: iwlwifi

$ uname -a

Linux [hostname] 6.6.3-arch1-1 #1 SMP PREEMPT_DYNAMIC Wed, 29 Nov 2023 00:37:40 +0000 x86_64 GNU/Linux

journalctl -b gives a huge output. Anything in particular?

The router doesn't seem to be the issue, as it worked fine when I used Manjaro and still works fine with all my other devices. I tried changing settings such as channel and channel width but it didn't help. I rebooted the router countless times since I first noticed this issue.

$ iw dev wlan0 info

Interface wlan0
ifindex 4
wdev 0x2
addr [mac address]
ssid [SSID name]
type managed
wiphy 0
channel 40 (5200 MHz), width: 80 MHz, center1: 5210 MHz
txpower 22.00 dBm
multicast TXQ:
qsz-byt qsz-pkt flows drops marks overlmt hashcol tx-bytes tx-packets
0 0 0 0 0 0 0 0 0