The evidence of UNRWA collaboration with Hamas came from captured computers, interrogations, surveillance camera pictures, and linking Gazans found dead in Israel on Oct. 7th and thereafter to UNRWA jobs. One of the released Israeli hostages swears he was held captive by an UNRWA teacher. I'm not sure the average layman will ever see the full write-up, but it was enough to convince the governments of the US, UK, EU, Japan, Germany, France, Italy, Sweden, Switzerland, Canada, Netherlands, Austria, Australia, Romania, Estonia, New Zealand (often very anti-Israel), and Iceland (typically HUGELY anti-Israel and more than a little antisemitic as well).
As for worker visas from Gaza - you won't have to worry about those ever again, and likely not for the West Bank either.
The ICJ ruling should please no one and there's an enormous amount of unrefined copium being slung around. There was no finding of Israel committing genocide, nor even an attempt at making such a finding or beginning an investigation, and no orders for them to cease operations. On the other side, the case wasn't thrown out altogether, as Israel had demanded, and the very suggestion makes them look utterly terrible and could be used as a pretext for diplomatic pullback. Hamas was ordered to release all hostages immediately (lol), Israel was ordered to take steps to make sure no genocide happened (which they are already doing), ordered to allow in humanitarian aid (also already happening), and ordered to investigate and prosecute any government officials who do issue calls for mass murder and genocide (such prosecutions would be a wholesale improvement and might even lead to the collapse of the Israeli government, inshallah). They are supposed to report back in a month, by which time Hamas will not have released the hostages and it's anyone's guess how the court will take that.
The most disgustingly ironic thing about the ICJ case is that - as I've written here repeatedly - the whole reason the Oct. 7th attack was possible was due to the shattering of Israeli society over Netanyahu's judicial overhaul. Netanyahu and his allies posed this as "returning power to the people" against an unaccountable permanent deep-state court system established by longtime Supreme Court justice Aharon Barak. You should look up some of the accusations the right-wingers launched at Aharon Barak. He was their George Soros and Hunter Biden all rolled up into one.
And when Israel gets pulled in front of the ICJ, who does Netanyahu appoint to speak on their behalf and legally argue against the charges? THE VERY SAME BARAK.