It's become something of a joke that Roll20's random number generator for dice doesn't seem to like the players much. The reality is that it's...well....probably averaging out where it realistically should, and the GM occasionally does see a bad streak of rolls too, but of course GMs get to roll a lot more dice over time so those bad luck streaks often die out soon enough.
In games that are player facing like Cypher System, you might think this would lead to better averages over time (or as many hills as valleys at least), but this doesn't always seem to work out. Some of my players are about fed up with Roll20, which can seem to give them alarmingly consistent failure streaks.
I have a theory about this, born of my own player experience in a related VTT, Astral. It goes like this:
Some players are cautious, and tend to build "average characters" who can do a lot of stuff reasonably well, but not much stuff very, very well. I'm often one of those....if you've ever built a Call of Cthulhu character, for example, who rarely had more than 50% in a skill, but also ended up with a lot of below 50% skills as a result, you might be one of these.
Other players suffer from a different problem: they don't really learn the game they are playing, or they miss the key elements of the system that help them out. These players might often try to do things and fail but miss opportunities to improve their odds of success or overlook strategies that could help them out. Some simply try to do things they probably shouldn't, or misunderstand their characters' abilities.
In VTT environments there's an entire other possible category: setting up your die scripts and forgetting modifiers of relevance. It's less common, as other players with better familiarity may catch your error, but it could happen.
A final category are: players who don't get the quirks of their GM. This one's pretty basic, but if you as a player know your GM frequently calls for history, society or perception tests then maybe you shoudl focus on those skills. This is a bit metagamist, but it's a valid strategy if your personal goal is "succeed at die roll tests more often."
Anyway, the result of these examples is players who fail more often than not at die rolls and are often quite flustered about it. I have at least one player who I feel is a combination of two or more of these situations, as he tends to learn the rules through play but overlooks the strategic elements of, as an example, how the die pool risk/reward mechanic of Cypher System plays out. If you play Cypher System like any other old RPG you are essentially doomed to failure. Conversely, when we play Pathfinder 2nd Edition I feel that most players (even the ones who are a bit shaky on the mechanics) tend to succeed about as often as you expect due to the fact that Pathfinder's probabilities and math are shockingly on target. If everyone is failing miserably in a Pathfinder 2E game on Roll20 it may say more about the GM than it does about the system or Roll20's RNG!
So what's a strategy for success? Well, here's some advice, and it may apply beyond VTT with virtual dice, too:
If you want to succeed, and your system allows it, try to find those 3-4 things you really want to be able to succeed in and max them out as best you can. If you're playing Call of Cthulhu and you want to spot hidden as often as possible then jam points in to it. You will sacrifice broad versatility but gain greater average success in those things you are good at. And it should go without saying: when you play the game, try to do things that are relevant to those skills!
Understand the game you are playing. Make sure you appreciate the probabilities so that when you are in combat or a tense encounter with die rolls that you think about your odds of success before you take on a task. Understand that if you make a Level 4 Speed Defense roll in Cypher without buying it down that the odds of failure are 55% but if you just spent some Speed you could reduce that failure rate to 40% or less. And when the dice still go against you....it's okay. You tried. The game is, ultimately, a game and not a wish fulfillment engine; we have video games for that.
As GM, make sure you are mindful of realistic encounters for your players' level of expertise and understanding. If your players seem to be struggling with understanding the mechanics (and the odds) then try to tailor the experience a bit as a teaching lesson. Coaching players with some learning encounters can be a wise move. Remember! You don't have a GM screen and you can't fudge dice in a VTT environment (well, not easily, as far as I know). As such, you need to respect the mechanics more, and the arbitrariness of the dice more.