Use compact view in File Explorer — via Winaero

The easy way

1. The easy way: File Explorer → View → Compact view.
2. Or: … → Options → View → tick Decrease space between items (compact view).

Registry change

Double-click a .reg file and confirm to merge it. Right-click → Edit first if you want to read it, which is always a good idea with any .reg file from the internet.

Apply

Windows Registry Editor Version 5.00

; Oddbyte.Me: Use compact view in File Explorer

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"UseCompactMode"=dword:00000001

Undo

Windows Registry Editor Version 5.00

; Oddbyte.Me: undo Use compact view in File Explorer

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced]
"UseCompactMode"=dword:00000000

Same thing from a command prompt

Run in a normal (non-admin) Command Prompt or Terminal.

reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced" /v "UseCompactMode" /t REG_DWORD /d 1 /f

Undo:

reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced" /v "UseCompactMode" /t REG_DWORD /d 0 /f

Some guides misspell the value as UseCompactView; the correct name is UseCompactMode. Close and reopen Explorer windows after the registry change.