We focus more on hackers, phishing attacks and stolen passwords but we don’t think about casinos employees who try’s to steal and manipulate our win.
Why would unscrupulous casino employees bother with small-time theft (like swiping our individual winnings) when they could potentially rob the entire casino? It seems to me that only a truly foolish scammer, one incapable of anything serious, would stoop to something like this. The most pathetic scammer in the world, working in a casino?

And how exactly would they manipulate the results? By lowering the RTP or influencing the outcome of a sporting event, for instance?

Has there ever been a documented case where casino staff stole user's winnings or manipulated the results? Personally, I’ve never come across anything like that in the public domain.
Some of the issues we have with casinos are not caused by the casino system that is put in place but because of the employees who are desperate and greedy.
Some of these casinos employees try to steal our win and if you don’t have enough evidence your money is gone, this is how some people lose their money and that’s why you need to gather evidence and keep when using a casino so you won’t be scammed by the casino’s employees.
What kind of evidence could a gambler possibly have? Only screenshots. If someone wanted to turn a gambler into a victim of scam, there are much easier ways to do it - for instance, by burying them in verification requests and checks, stalling the withdrawal process, or refusing to pay out a prize under some trumped-up pretext.
I will like to ask all of you, do you believe online casinos have enough internal security to prevent employees from abusing their access?
Ideally, a casino should have an internal security department tasked with preventing abuses. However, smaller casinos may lack this due to limited budgets. This is yet another reason to stick exclusively to large, well-established casinos with a proven track record - those capable of maintaining a robust security team.