How to set up a new computer
$ iw wlan0 get power_save
Power save: on
As you see, it is power_save on; it is enabled. One may wonder what sort of thinking led to a default setting of power save enabled on a device that is plugged into a mains outlet, but it is a mind fart that should probably be disabled on the Raspberry Pi.
One way to accomplish this is to build a systemd unit file which can execute the necessary command at boot. I will give you here a bit more comfortable example for switching off or on power_save. Create a Unit file with:
rpi ~$ sudo systemctl --full --force edit wifi_powersave@.service
In the empty editor insert these statements, save them and quit the editor:
[Unit]
Description=Set WiFi power save %i
After=sys-subsystem-net-devices-wlan0.device
[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/sbin/iw dev wlan0 set power_save %i
[Install]
WantedBy=sys-subsystem-net-devices-wlan0.device
Now enable just what you want on boot up:
rpi ~$ sudo systemctl disable wifi_powersave@off.service
rpi ~$ sudo systemctl enable wifi_powersave@on.service
# or
rpi ~$ sudo systemctl disable wifi_powersave@on.service
rpi ~$ sudo systemctl enable wifi_powersave@off.service