Why am I getting slow speeds when a Linux machine as Wi-Fi AP?

I’m using a Raspberry Pi 5 as a Wi‑Fi bridge (AP for my laptop + STA to dorm Wi‑Fi). I expected laptop speeds to approach the Pi’s WAN speed, but there’s a ~40 Mbps gap I can’t explain. My setup Raspberry Pi 5 with Debian trixie, kernel 6.12.47+rpt-rpi-2712 wlan1 (Edimax EW‑7811UTC) connects to dorm Wi‑Fi wlan0 (internal) hosts AP NAT/forwarding enabled (NetworkManager ipv4.method=shared, ipv4.ip_forward=1, nftables masquerade) Commands I used to set up the AP + NAT AP (wlan0), 5 GHz, 80 MHz, NAT/shared sudo nmcli con add type wifi ifname wlan0 con-name Hotspot autoconnect yes ssid PiAP sudo n

Question by ollo on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.