Linux 5.4.3 - VS Code Intellisense seemingly not catching errors nor is autocomplete functioning

You will get none of the niceties when using VS Code unfortunately.

If you want (accurate) compile errors, you need to compile.
Autocomplete is a complete mess, you can try using the tag parser but that is not context sensitive and will make bad suggestions.
A quick search suggests this may work, seems it hasn’t been updated in a while now though.

If these things are important to you, or you intend to do a lot of C++ in Unreal, you will want to fork out for Rider.