Per the
https://www.mysouthshoreline.com/ website, bikes on trains will end on Monday, October 31st. The program only runs April-October and (as noted) is limited to high platform stations where the center doors of the special bike carrying cars can open and (as noted for construction) was limited this year to stations west of and including East Chicago. (East Chicago is the last station with a high platform west of Gary - all trains are being bused east of Gary to Michigan City with separate trains running from Michigan City to South Bend.)
Portage is low platform (but is getting a high platform next year). Ogden Dunes is the most popular high platform stop for bikes. The new Michigan City 11th St station will be getting high platforms when it reopens. So even before construction both Portage and Michigan City would be no go for bikes. Check back in 2024.