Like re-released as like a 4-disc CD Gold Best Hits Mega Dance collection from the 1980s?! What on earth are you talking about “remastered?”
The “autocompletion” you speak of is called Intellisense. Like most software, it may malfunction and need to be coddled and coaxed back into useful behavior. This should not be a surprise to you, since you have been here for several years already.
This may help you with intellisense and possibly other Visual Studio integration problems:
Sometimes the fix is as simple as doing Assets → Open C# Project from Unity. Other times it requires more.
Other times it requires you also nuke the userprefs and .vsconfig and other crufty low-value high-hassle files that Visual Studio tends to slowly damage over time, then try the above trick.
Barring all that, move on to other ideas:
https://discussions.unity.com/t/778503
Also, try update the VSCode package inside of Unity: Window → Package Manager → Search for Visual Studio Code Editor → Press the Update button
Also, this: https://discussions.unity.com/t/805330/7