In general, if Apple says a new OS can run on your Mac, then it should run as well as older versions. One of the reasons they cut off older Macs is because they can’t get or guarantee decent performance.
Definitely have a look at Activity Monitor: see what processes are using the most CPU and memory. What’s your RAM usage? (Bear in mind that with only 8Gb, macOS will use it all — but how is it being used? What’s the memory pressure, and how much swap?)
Also, make sure that any third-party Launch Agents, Login Items, and other ‘background’ processes are up-to-date and compatible with the new OS. You could also try clearing caches (boot to Safe Boot mode, and out again.)
Also, you say you’ve upgraded VSCode. Any chance that the new version (and other software you’re running) is just more demanding? Let’s face it, a 2-core 8Gb Air is not the development tool of choice, even in 2017.
