Amtrak unfortunately removed the timetables from their website, sometime in mid-March once they began to reduce service because of COVID. If you want to look through the most recent ones in late 2019 and early 2020, it seems that they are all still up on the Juckins website, on this page: Amtrak Timetable Archives - Home
Note too to check which trains are still running, that you would need to do a reservation search on Amtrak's website. Many regional trains are running at reduced levels(i.e. Hiawatha, Michigan Service trains, Illini/Saluki, Missouri River Runner, etc), and a few still haven't been brought back into service(i.e. Pere Marquette).