There is no checkbox for it and no menu item, nor any tucked-away pane in Finder => Settings. If you want to see dotfiles in Finder, Apple expects you to either know a keyboard shortcut or drop into the terminal... meeeh.
The shortcut
In any Finder window press...
Cmd + Shift + .Hidden files appear. Press it again, they disappear. That's it, that is the entire UI. Really? 😳
The permanent version
If you want hidden files always shown, set a default and reload Finder. Run the following in your shell/terminal...
defaults write com.apple.finder AppleShowAllFiles -bool true... followed by
killall FinderTo revert, set it to false and killall Finder again.
Why this isn't in the UI
My best guess... Apple doesn't want regular users poking at .DS_Store, .Trashes, or anything else prefixed with a dot. The shortcut exists for the people who need it; the absence of a menu toggle is the design decision, not an oversight.
It's a fair call, but it's worth knowing the toggle exists, because once you've seen a .env file half-deleted by Time Machine, you start wanting visibility on the things macOS hides by default.
