The only one I have seen so far is the demo of "The Pedestrian", here: https://www.speedrun.com/theped#Demo_Any
I guess you won't have much luck finding many of those on the site. If a game is out, no one will speedrun the demo, they will go to the full game instead. Demos of future games will probably not be accepted to the site at all anymore, because of some newer rules in the "Game request" section.
In the case of the pedestrian game, the demo was requested (and accepted into the site) 2 years ago. Then only recently the leaderboard became focused on the full game after it was out, and the demo leaderboard turned into a misc category.
That's not how this works. If anyone else wants to submit a game request, they have to speedrun the game themselves, first. You have ran the game yourself, I assume? Your YouTube link isn't working.
Anyway, you better just wait those 7 days. In the meantime, you can run another game, or continue running your game and try to improve your times.
Hmm, I'm not sure about the exact meaning of "720p threshold" phrase in that rule.
There is no hard requirement for resolutions. Some games specifically require a good quality so the viewer can see certain aspects of the video clearly, like an ingame timer. In any case, low quality video might get your run rejected.
Generally, you run should be with a good enough video quality so the viewer can see clearly what is going on. This can happen with resolution of 360p or more (although 480p is better). Lower than that (240/120) is bad quality and makes the video look really bad, don't do that please.
Some games also require a specific video framerate (30fps or 60fps), but it isn't common and you shouldn't worry about it.
Also, I always record in 1080p/60fps, and never got file size more than 1-2 GB on a 30 minute video. So, I guess this is a longer game? if you record in OBS, you can adjust the file size in the settings, as well as tinker with the resolution.
EDIT: I just realized that the rules you read (Moderation rules) are not meant for a game request to the site (which is done by the site staff). Those are general guidelines and rules for the game moderators themselves, as to how they should set and handle their games.
First of all, welcome to the speedrunning community! For Volgaar the Viking guides and information, you can start with the game leaderboard here: https://www.speedrun.com/volgarr_the_viking Feel free to ask questions on the game in that forum, the game moderators and runners can help you. You can read the guides there, and also watch some of the runs of other runners to see what they are doing, and learn from them.
Don't worry about the game not being "famous". Seeing that around 30 people have ran this game so far, this game is much more popular/known than many other games in this site (or at least it was, seeing no one submitted a run recently).
Another thing, a common advice here is to speedrun a game that you love. It will help you start running and not getting bored quickly. So it's all up to you. If you like playing the game, it is a good choice.
Good luck on your speedruns :)
Better ask in the forums of the game itself, the game moderators/runners can answer that more easily. https://www.speedrun.com/jaws/forum