Tapping anywhere resets the video to beginning. There's no way to go forward or back. Even the most basic html insert allows for control of the video. This may be a mobile only issue.

The "red dot" on the timeline is your friend.
If you put your fingertip on it, you can scroll through the timeline - back and forth.

Apart from that: on mobile, you should be able to double-tap left or right of the center of the screen, to jump a few seconds backwards or forward (default is 10 seconds).

You can also change the duration of the jumps.
Simply click on:
your profile pic --> settings --> general --> double-tap to seek --> select a timeframe between 5 and 60 seconds.

I know what you mean, and yes, it is a mobile only issue. My phone does the same. Once the video starts playing, there is no way to interact with it and the moment you touch the screen, it terminates playback and shows thumbnail again. Might be browser dependent, but I gave up on watching vids on GOG on my phone.

As for the advice above, nothing of that works. The playback UI never shows up (no progress bar/dot, video controls or even the video name text etc.) and double tapping can't be done because the first tap instantly cancels playback.

Which OS and how old of a mobile device? Because this is the first I ever heard of this problem.

Me personally, Samsung Internet, phone is from 2019. All I can do is start and stop the video by tapping on it and stopping it resets it back to start.

What GOG video exactly? I'd love to try and recreate the issue.
I just tried again on mobile, and I can scroll through the timeline and double-tap to jump through the video just like it is intended, and as I described it in my initial post.
On Android 12.

Doesn't really matter. Any video that is in the carousel with the screenshots. I'm on Android 11.

Then again, I last updated the phone a year ago, so could be that :P

Ah, I see...funny (well, weird, rather).

If I watch the videos directly on GOG, and try to scroll/double-tab forward, I experience the same issue.

But if I watch the same videos directly on YouTube, the issue doesn't exist (for me).

Yep. Normally watching the vids on Youtube is without issues. But I am pretty sure OP meant the embedded video player here on GOG.

you should be able to double-tap left or right of the center in ssstik.io/id of the screen, to jump a few seconds backwards or forward

It's been a problem forever for me. I've had at least 3 or 4 different phones, Android versions. Current device is Pixel 6a with vanilla Android 12. It's impossible to get to any controls. As posted by another user in this thread, as soon as tap anywhere in the video window it stops the video and resets it to the beginning.

When I first saw this I thought it was about youtube, but seeing how it's a problem on gog it makes sense now.

Your average 5th grader can put a youTube video in a website and have it play properly. An impossible task for GoG. I remember they used to not even play at all on Android. It took them literally a year to get the problem fixed. Welcome to GoG.