Spoiler-free : Are there points of no return for progressing the game/quest storylines?
Solution 1:
There are two major points of no return
After obtaining the Lotus of the Palace and the Shelter stone
Once both of these items have been obtained, you'll no longer be able to make progress towards one of the special endings, and you'll also lose the ability to fast travel to Ashina Castle (you're able to re-explore the area to unlock the shrines again). After reaching a certain boss in this area you get two choices,
you'll be given a choice to "follow" or "break" the iron code,
Choosing the first option also acts as a point of no return as you immediately go into one of the games special endings.
After defeating the Divine Dragon.
Once this boss is defeated, you're officially in endgame and a lot of content becomes inaccessible, including steps towards two of the special endings and several character quest lines.
As usual in From Software games, some character quest lines intersect at certain points, so there are a few points within certain quests that cut off access to other quest line endings, but that's a whole lot more spoilery~