Message from Munich Airport homepage:
From October 23 (10:30 p.m.) through November 13 (4 a.m.), rail services to Munich Airport will be disrupted due to construction works. There will be interruptions on both suburban train (S-Bahn) lines S1 and S8 as well as on regional services during this period.
A rail replacement service will be provided.
DB travel planer/App (https://int.bahn.de/en) or MVV travel planer (https://efa.mvv-muenchen.de/index.html) will show the alternative routes.
Travel will take about 20 to 30 minutes longer than usually.