On Windows, I found this command worked

# powershell
Get-CimInstance Win32_LogonSession

The StartTime is the time you logged in. If there are two many entries try

(Get-CimInstance Win32_LogonSession | where {$_.LogonType -eq 2})

A command that works on home installs (when you’re not in a Windows DOMAIN) is

net user %username%

But, for me, when on a corporate login, this didn’t work. ALSO NOTE: In some environments the net command is disabled for normal users.

On Linux how can I find when I last logged in?

On Unix, I can run the last command to find my last login.

last $USER
username  tty  host  login_time - logout_time  (duration)