There is no simple answer to the question of whether or not online poker can be rigged. While there have been some isolated incidents of cheating, it is generally very difficult to rig an online poker game. The most likely scenario in which online poker could be rigged would be if a site were to allow players to collude with each other or to use bots to play on their behalf. However, most reputable online poker sites have measures in place to prevent these kinds of activities from taking place.
If you're concerned that a particular online poker site might be rigged, the best thing to do is to research the site's reputation and look for any player complaints about unfairness. If you can't find anything concrete, then it's probably safe to assume that the site is fair. However, it's always best to err on the side of caution and only play at sites that you trust.
Modern-era players enjoy access to a wealth of poker database software that can keep track of every hand played at some poker rooms. This data can be used to look for patterns that might indicate cheating. Some sites also make use of random number generators to ensure that each hand is truly random.
Overall, it's very unlikely that you'll encounter any rigging when playing online poker. However, it's always important to be aware of the possibility and to take steps to protect yourself. Only play at reputable sites, and be sure to pay attention to your own gameplay. If you suspect that something might be wrong, don't hesitate to contact customer service or report the issue to the site's administrators.