I'm guessing you are running OctoPi (you didn't say for some unknown reason....)
The webcam server mjpg-streamer as bundled on OctoPi has been shipping without the control page for a while now (0.16 maybe?) since it doesn't secure said page and it therefore can be considered a security risk to have it enabled.
Is the control.html page available in the current nightly build?
Just installed fresh 2020-09-23_2020-08-20-octopi-buster-armhf-lite-0.18.0.zip and there is available only index file at http://<ip:>8080/ with latest snapshot and live stream.
pi@octopi:~ $ cat /var/log/webcamd.log
Starting up webcamDaemon...
--- Configuration: ----------------------------
cfg_file: /boot/octopi.txt
camera: raspi
usb options: -r 640x480 -f 10
raspi options: -x 1280 -y 720 -fps 20
http options: -w ./www
Explicitly USB device:
-----------------------------------------------
Found video devices:
/dev/video0
/dev/video10
/dev/video11
/dev/video12
/dev/video13
/dev/video14
/dev/video15
/dev/video16
raspi
config file='/boot/octopi.txt':Start MJPG-streamer with video device: raspi
<13>Sep 23 18:46:54 root: Starting Raspberry Pi camera
Checking for VL805 (Raspberry Pi 4)...
- It seems that you don't have VL805 (Raspberry Pi 4).
There should be no problems with USB (a.k.a. select() timeout)
Running ./mjpg_streamer -o output_http.so -w ./www -i input_raspicam.so -x 1280 -y 720 -fps 20
MJPG Streamer Version: git rev: 85f89a8c321e799fabb1693c5d133f3fb48ee748
i: fps.............: 20
i: resolution........: 1280 x 720
i: camera parameters..............:
Sharpness 0, Contrast 0, Brightness 50
Saturation 0, ISO 0, Video Stabilisation No, Exposure compensation 0
Exposure Mode 'auto', AWB Mode 'auto', Image Effect 'none'
Metering Mode 'average', Colour Effect Enabled No with U = 128, V = 128
Rotation 0, hflip No, vflip No
ROI x 0.000000, y 0.000000, w 1.000000 h 1.000000
o: www-folder-path......: ./www/
o: HTTP TCP port........: 8080
o: HTTP Listen Address..: (null)
o: username:password....: disabled
o: commands.............: enabled
i: Starting Camera
Encoder Buffer Size 81920
Done bring up all configured video device
Goodbye...
It's not just the mjpegstreamer options. the raspberry pi mjpgstreamer .so does NOT implement the control page. The trick is to load the official raspicam driver on boot and to switch to the regular usb cam module. See this comment from another thread:
You probably know this, but for anyone else reading this thread, TSD and OctoPrint Anywhere have a clever built in streamer that uses modern compression. However, there are no controls built-in (brightness, bitrate, etc...), so it's a tradeoff.