is the s-bahn from frankfurt to offenbach fully operational?
I believe so. I think they've had some minor disruptions (mostly with late night routes), but it's generally operational. You can check here: https://verkehrslage.bahnhof.de/en/region/DB_SBahn_RheinMain?f=0!mwfzxs00!mwq00qnz!1!1!1!0!u0!1ltm5v!aoqvlh