I don't think the dummy target approach adequately works for fast lenses (especially on full frame) and images viewed on a high-resolution screen where the depth of field can be mere centimeters. It may work adequately for a slow crop sensor kit zoom.
I'm not sure if 77D has this feature, but the EOS RP, which I recently bought, has an interval timer feature. For example, you can set an interval timer for 00:00:20 interval and 5 shots. When you press the shutter, the first picture is taken and then the camera will take the next pictures according to the interval you specified.
I just tested this "interval timer" feature on my EOS RP, and even in the one-shot AF mode (as opposed to servo AF), the interval timer autofocuses automatically prior to taking each picture. My test involved putting one object close to the camera and the other object twice as far from the camera. Then I alternately removed the close object and put it back. The nearest object in the scene was always the one the camera chose to focus at (both objects were around the autofocus point).
Note the interval timer is set in the camera menu. It's distinct from the self-timer (that can be set to take a picture after 2 seconds, take a picture after 10 seconds, or to take a burst of pictures after 10 seconds). If using the self-timer, focusing happens when half-pressing the shutter, so there's no option to focus after the timer expires. Also, self-timer has the drawback that you only have the choice between 2 and 10 seconds. Interval timer allows an arbitrary timer period.
Even the manual acknowledges this feature, but for some reason it suggests manual focusing: "Setting the lens focus mode switch to
<AF> prevents the camera from shooting unless subjects are in focus. Setting it to
<MF> and focusing manually before shooting is recommended."
Now, does 77D have this feature? I don't know. My cheap EOS 2000D certainly doesn't.
If you want to take a quick burst, you'll probably want an interval of 00:00:01 and then to take 30 shots. You then just delete the shots where you were walking from the camera controls to the scene.
Also, some cameras (like 2000D and EOS RP) can act as a Wi-Fi access point, allowing remote release using the Canon Android app. Then you just connect your smartphone to the camera, set up the camera (use selfie timer here so that you have time to put the phone to your pocket) and tripod, walk to the scene, use remote shutter release in the app, put the phone to the pocket during the self-timer and wait for the timer to expire. The app can show live view picture from the camera, so no tiltie-flippie LCD screen required.
If using Wi-Fi, remember to turn it off from the camera (not just from the phone!) before connecting the camera via USB to a computer, as the USB may not work with Wi-Fi enabled.