EDIT: and if you're wondering where the initial exposure to Roblox came from, it was from an Android tablet I had at the time which was setup strictly for kids games (hence the FamilyLink with time limits and stuff)
I don't want to kick you when you're down, but you tried a technical solution on a human problem.
I've see parents "talk" with their children, where it seemed more like they were talking _at_ them. I could see in the kids face he was putting on a show of listening (and pretending to go along with it), because that was the fastest track to going back to doing whatever he liked when they weren't watching.
Where it worked though, was getting closer to my children by admitting where I was at and where I was coming from. When they feel like you're really connecting with them.
I'm sure my kids still get up to much I'll (hopefully) never hear about, but that's normal. As long as the big overarching stuff is understood, I'll take that as a win.
I also gave lectures and installed FamilyLink and put restrictions on my router to prevent my child from accessing devices in a way I didn't approve of or when I couldn't adequately supervise it. The sneaky little shit still found ways to circumvent all this both here at home and at school. My child completely ignored all the warnings and eventually got roped into talking to a very sick predatory individual over Roblox.
The Roblox creep convinced my child to sign up for Instagram where they were able to get on video calls often. They then made my child watch them do very disturbing things, including attempting to hang themselves, cutting themselves open, and other very sick shit that I would have never imagined. They then threatened my child that if it was reported, they would kill our entire family. This went on for a couple of years apparently and we're still dealing with the trauma and fallout of it years later. Authorities were unable to determine the identity of the individual due to the many layers of obfuscation (fake names, VPN usage, etc).
I'm a software engineer of nearly 20 years and very knowledgeable of tech. The fact that this still happened despite my many roadblocks and safe-guards I put in place really shocked me to the core. Not to mention the whole "am I terrible parent" question which naturally arises out of all this. I've been reassured that I did everything I could reasonably do to prevent it, but that question always weighs on my mind regardless.
I warn every parent I can to keep their kids off Roblox and other "community driven" games that are like this.