I don't know but It does for other plone4 instances, but on Plone6 if I print the request, I can't see it.
I'm using the classic
RewriteRule ^/mysite(.*) <virtual host root versus the plone instance etc etc>$1 [L,P,E=remoteUser:%{LA-U:REMOTE_USER}]
but when I print the request (with a pythonscript), no trace of remoteUser neither REMOTE_USER nor HTTP_X_REMOTE_USER (I don't see anything coming from the autenticated shibbolet session, just the cookie).
And I can see variables set with
RequestHeader set A_VAR: a_value
so the variables are passed.
UPDATE [SOLVED]: I've just discovered that variables starting with X_ are removed in Plone6 while they're not in Plone4. And guess, all the variables from shibboleth mapping starts with X_ 