See also:
Console Virtual Terminal Sequences
Starting in PowerShell 5.1, the PowerShell console supports VT escape sequences that can be used to position and format console text. Note that this
# Enable underline
$esc = [char]27
"$esc[4mOutput is now underlined!"
# Disable underline
$esc = [char]27
"$esc[0mReset"
Or as pointed out already, with Write-Host, just switch the text color inline for contrast...
Write-Host -ForegroundColor gray 'This is not bold ' -NoNewline
Write-Host -ForegroundColor White 'This is Bold ' -NoNewline
Write-Host -ForegroundColor gray 'This is not bold'
... that is if you did not download or can't download and use external stuff.