Outlook uses windows timezones when exporting calendar in ICS format. Meanwhile the rest of the world uses the IANA time zone database.
Windows timezone:
DTSTART;TZID=Eastern Standard Time:20200424T090000
DTEND;TZID=Eastern Standard Time:20200503T21000
IANA timezone:
DTSTART;TZID=America/New_York:20200424T090000
DTEND;TZID=America/New_York:20200503T21000