nah

that's some age old struggle

idk how people still justify that clusterfuck, but it's that way since forever. I remember vividly how we were annoyed by such shit with some "cross platform" gui toolkits (or browsers) back when debian woody still was relevant.

This won't be solved in this decade. or the next.

There's a bug open for Firefox and you can change VSCode's behavior by putting this in your keybindings.json:

{
    "key": "shift+insert",
    "command": "editor.action.selectionClipboardPaste",
    "when": "textInputFocus && !editorReadonly"
}

Not sure why either of them are messing with a "standard" shortcut...
If you want a more system-wide solution there are utilities that let you sync the PRIMARY (on selection) and CLIPBOARD (Ctrl+c) buffers mentioned in the Arch Wiki entry.

If you merge CLIPBOARD and PRIMARY, every time you select text, you'll wipe out the contents of CLIPBOARD. You won't be able to copy text, then do any work that involves selecting text, then paste.

Such stupidity, this drives me nuts

autocutsel -cutbuffer 0 -f -s PRIMARY
autocutsel -f -s CLIPBOARD