Just to clarify something, VSCode is Visual Studio Code, a desktop application that is a “lightweight Visual Studio for Code”. Microsoft has ALSO launched https://vscode.dev/, which is “Visual Studio Code for the Web”, a free “zero install” online version of VS Code that runs in the browser. See: Visual Studio Code for the Web
You could try my TW5-Syntax plugin by launching https://vscode.dev/, clicking “Extensions” in the far-left bar (it’s the 4 blocks icon), and typing TiddlyWiki into search. Select “Tiddlywiki Syntax” (2nd result), and click Install.
Then open a new file by selecting the three-line “hamburger” button on the top of the left-bar, File → New File. Change the type to “Tiddlywiki5” by selecting “Plain Text” in the bottom status bar, typing “tid” into the open search popup, and choosing “Tiddlywiki5” (not “tid” or “multitid”).
Then go to https://tiddlywiki.com/#%24%3A%2Fcore%2Fui%2FEditTemplate (for example) and copy/paste the wikicode into the new editor-file.