Disable mouse side button Alt-Tab behavior in Windows 10

A Bluetooth device may send commands to windows without the OS knowing the physical properties of the device. So there's no way such behaviour could be controlled through the OS. Only the behaviour of the standard mouse buttons (left, right, wheel) can be controlled directly through the OS: these are the only buttons which are common across all manufaturers.

Personally, I am using the "Logitech Options" software, which is availabel also for your M270. I would not at all call it a crapware, but an essential piece of software to get the most out of your mouse. It is lightweight and has practically no system impact. It will allow you to tune your mouse exactly to your needs. In many situations, exact mouse tuning can considerably speed up your workflow.

Here's a screenshot of typical system impact:

Consider "Logitech Options" more like a manufacturer-specific DRIVER for your device, which happens to have a user interface. Like with any hardware, if you don't install the specific driver, not all functions of your hardware will be available. The difference with an IntelliPoint mouse is that the IntelliPoint driver is tied differently to the OS and can be opened through the System settings. You can't do that with Logitech Options. But at the end of the day, the impact on your system will be similar, since every driver always will have a (minnimal) impact on your system.