Some system extensions will not be compatible with a future version of macOS.

There is nothing you have to do or be worried about. What Apple is telling us is that when the next new operating system comes out, it will no longer allow those Legacy System Extensions. That means that any software vendors who have failed to update their offerings will be incompatible with the new OS. Those vendors have all been told what changes they will need to make to be compatible and I assume they are doing so. The bottom line is this. Before installing the next OS, Bug Sur, we need to visit our vendor web sites to verify that they have updated their offerings. If an important software has not been upgraded, then it might be a good idea to wait before installing Big Sur. At this time, it is expected that Big Sur is expected to be released late summer sometime. We will have to see how it all plays out.

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 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.

You're welcome. :)