Just to summarize so it is summarized somewhere:
H2H matchups that end Sunday will not be extended.
The Ottoneu season will be extended as necessary to cover all MLB regular season games, which includes tiebreaker games, etc. This will extend season-long leagues.
Waivers and auctions will correspondingly be extended to be available/active through the entire MLB regular season. If there’s a game on Monday, auctions will have to be wrapped by 11:59pm ET Monday instead of 11:59pm ET Sunday.
There are more details in the threads I’ve shared in the previous post but I believe this is a full summary.