Sooo I started doing speedruns of this game a little while ago, but I've never completed any run of this game mostly because of the SCP-914, I most of the time spend 30 seconds to 1 minute trying to get an Omni Card/Level 5 Card, I keep loading save files, and these cards never show up, and in the end I just give up.

Is there something you can do to higher your chances of getting an Omni Card/Level 5 Card? Or it's just completely random?

the more achievements you have the better your chances are to getting them. Or be like me, just upgrade a level 2 to level 5 and make sure to save when putting your lvl 3 on fine. because it will either be a playing card or a level 4 so just do the same save reload.

*edit: i was wrong

Taking longer than 30 seconds is quite normal for omni. Omni is a ~1/108 per card. The strat I recommend beginner runners do is to grab the extra card in the infinite hallway, as shown in the video here:

This will bring the chances of getting an omni to around a 1/36 per load.

Omni probabiliy is slightly complex than just 1/N chance. It depends only on two factors: game difficulty and obtained achievements.

Omni chance is defined by formula ((MAXACHIEVEMENTS-1) x difficultyFactor)-((CurrAchvAmount-1) × 3) Where difficulty factors are: SAFE = 3 EUCLID = 4 KETER = 5

For example, I have 31/37 obtained achievements and playing on Keter. So, now I have 1 / 90 chance to get omni from my key card.

I got this formula from source code: https://github.com/Regalis11/scpcb/blob/master/Main.bb#L9722

You are correct: I just used the 1/108 per card because it's the odds you're most likely to have in a speedrun.