The fundamental challenge with collectible card games is that your ceiling as a player is predicated by the cards you have. Even the best players will lose to average players if the power gap between decks is wide enough.
For newbies, the struggle is even worse. The combination of being short on game knowledge and powerful cards is an incredibly steep (and expensive) hole to climb out of. As a newcomer to Pokemon TCG Online, my pre-made decks would routinely get stomped out by players who had every GX/V/VMax card imaginable. Above and beyond learning how to play the game, it’s going to take some combination of time and money – probably lots of both – to avoid losing every match in Standard or Expanded format.
Thankfully, there exists salvation for newcomers, scrubs, and those who want to play Pokemon TCG Online with a more rigid set of balance boundaries. If this sounds more up your alley, then the Theme format is your battlefield of choice.