Hey man, my son got this keyboard today and was having the same exact issue and it was wracking out heck out of me. I was able to figure it out.

Disclaimer: I feel that after the second step of removing the xbox controller, it may work and you should be fine. Why do I say this? Because, because based off of another post I saw from a while back I actually tried steps 3 and 4 the first time around without seeing the xbox controller device in device manager and wasn’t successful in removing the controller issue from Roblox when I booted it up. It wasn’t until my 2nd attempt that I found the Xbox controller device, disable it and the controller was removed, so it’s logical to think that the 1st and 2nd step would solve your problem. 

1. The first thing I did was update the driver, which us kind of silly they dont include this in the setup options. This can be downloaded here:  NOTE: Pay attention to the model you bought (again, silly they didnt incorporate it into one single driver updater app)
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     • Razer Huntsman V3 Pro Mini Firmware Updater | RZ03-0499

     • Razer Huntsman V3 Pro Firmware Updater | RZ03-0497

     • Razer Huntsman V3 Pro TKL Firmware Updater | RZ03-0498

2. After installed, go to your Device Manager by right clicking the windows start icon on the taskbar, go to the bottom and see if it has an Xbox Controller, if so, click it and it show the device, right click the device and disable it. It may ask you to restart your computer, don’t. Try to boot up Roblox and see if it goes away….. ( If this fixes the issue don’t bother with the rest, if it doesn’t, keep on reading then)
3. Next, Also in the Device Manager, find “Human Interface Device” - mine had a bunch but you are looking for the one that says “Human Interface Game Device”they all look similar, just look for the one(s) that have the word “game” in them, select them, right click them, and disable. Try to boot up Roblox and see if it goes away….. ( If this fixes the issue don’t bother with the rest, if it doesn’t, keep on reading then)
4. Left click start, left click settings, go to Bluetooth & other devices, select the Huntsmen V3 Pro Keyboard, if it shows a “Driver Error” message, select remove device, unplug the keyboard after you see it is removed, it stays in the “removing” state for too long, just unplug it and plug it back in.

Hope it works out for you! 

Thank you so much, the 2nd option worked for me.

If your razer huntsman mini says “controller mode (gamepad) activated” when playing Roblox, read this. After struggling with this for a while i found a solution, first you want to open “device manager” scroll down to “Human Interface Device”, when you’re there you want to scroll until finding “razer huntsman mini controller” right click and press delete. I hope you found this helpful, if not sorry.

in case some are still looking for alternate solutions, you can try going in your synapse 3, then select your keyboard, go to on-board profile, then select "Factory Default”. Do this every time you need to remove the "controller” mode of the keyboard, to play older video games or if you are having conflicts with your other controller.

BTW, in case you did some tweaking in the software or used some programs to disable Razers control functions, (like xbox360ce, devreorder, HIDhide Configuration Client, etc), I highly suggest you to restore everything to default settings before trying this.

P.S. for reference, I am using Huntsman V3 Pro (the full keyboard)

this one worked for me! thank you so much!!!!

none of these have helped me i cant seem to find the inteface human device named Huntsman controller i can only see the keyboard

​@bestvilleCoralRed374 u r the best i been here searching for solution  for hours