How to block Razer Synapse installer on Windows 10
Hi, I bought a Razer Deathadder mouse and wanted to use it as a normal mouse without the extra functions but the Razer Synapse installer kept popping up every time I plugged in the mouse or restarted. Below is how I fixed it. This was written in September 2020 in case someone is reading this in the far future.

Based on my understanding this is happening because any time you plug in a new device Windows tries to find and install the drivers for the new device you plugged in. It just so happens that the Razer Synapse installer is the "driver" that Windows keeps picking up and trying to install for your Razer peripheral. During installation a folder is created in the OS files with all the installation files inside it. We are going to find this folder, delete this folder, create a new folder with the exact same name, and lock this new empty folder so Windows can't put any installation files in it when it tries to install Razer's "driver." Make sure you are using an administrator account, otherwise you won't be able to do this.
Step 1: Open File Explorer
Step 2: Go to the directory C:\Windows\Installer
Step 3: Right-click the Razer folder and click Delete (this folder has all the Razer Synapse installation files)
Step 4: Right-click inside the Installer folder > New > Folder
Step 5: Name the new folder you made "Razer"
Step 6: Right-click on the new Razer folder > Properties
Step 7: In the properties: Go to the Securty tab, then click Edit...
Step 8: Select the SYSTEM user, check the Deny box on the Write permission, click Apply (you will get a bunch of scary warnings, just accept them, you are not locking your personal files or anything), and then click OK. You should be done at this point.
I hope this fixes your Razer Synapse installer problem. Have fun.