how do I remove Kernel Extensions?

I think Apple did a very poor job of explaining this. But hopefully they handle it better once it happens.

You should always wait a few iterations of a new OS to get the bugs worked out, that's likely a year from now!

No need to worry, but to see them, just don't upgrade to 10.16 or iOSXi, or whatever Big Sur is if the developers don't have updates...

About this Mac>System Report>Software>Extensions, click on Obtained from Header, all that aren't Apple are Legacy.

I think Apple did a very poor job of explaining this.

Without a doubt. It's as bad as the message for 32 bit software that very vaguely said you had launched software that is not compatible, and may not work in a future OS.

The messaging would've been better if renaming 10.16 to 11 weren't a late-breaking decision.

Had they put a stake in the road saying "the next release will be MacOS 11", they could've made the messaging about "these kexts won't work with MacOS 11, the next major release of MacOS" -- years in advance. Major breakage, like deprecating 32-bit apps and kexts, shouldn't break with 10.x updates. I think Apple learned all the wrong lessons from PowerPC->Intel.. :(

Why do you want to? Are you sure it's not for software you're using, that if you do remove the extension, it will stop working?

The next major release of macOS (Big Sur) will not allow third party kernel extensions. It's just warning that any third party software you're using that installs such extensions will not work in macOS 11.

All vendors who now user kernel extensions will have to use a different method to load items at startup.

https://support.apple.com/en-us/HT210999

The message should have mentioned the name of the vendor the extension is from. But in short, all third party extensions are in the following location, along with ten default extensions installed with the OS.

/Library/Extensions

Of those you find in this folder, the following are installed by the OS. Any others would have been added by third party software you installed.

ACS6x.kext

ArcMSR.kext

ATTOCelerityFC8.kext

ATTOExpressSASHBA2.kext

ATTOExpressSASRAID2.kext

CalDigitHDProDrv.kext

HighPointIOP.kext

HighPointRR.kext

PromiseSTEX.kext

SoftRAID.kext

For now, you don't need to do anything.