I mean, you can't get a warning that the `[]` syntax isn't available in your old codebase's flavor of PHP (5.2) in VS Code. I think.
Alternatively: Take time off. If you have enough money to live on for a month, take it. Make a list of things you'd like to dig into, or just spend a month doodling. Or take half days off for a month and participate in something like Advent of Code. You can challenge yourself in various ways, like use an unfamiliar language for the month, or a different language every day. Do some tutorials and make stuff in Pico-8, embrace the limitations and embarrassingly unreadable code, which is amazing at the same time because you wrote it and it all fits in your head. Just throwing it out there.