I wasn't all that far into Dragon Age: The Veilguard when I realised I'd been locked out of a sidequest unexpectedly. It was after the first significant event in the game where you, of course, have to make a big decision that has some longer-lasting repercussions. But if you're not paying attention to your quest log, you might not notice that some quests disappear into the completed section with a little entry above them saying something along the lines of "You can no longer complete this because this event has happened".
This occurs throughout the game, and in-particular, affects faction and companion quests—essentially the two most important quest types for if you want to gain allies, faction reputation, or even romance a specific character in the game. One to look out for in-particular is Taash.
- A Warden's Best Friend: Complete A Slow Poison before this plus any follow up quests
- A Change On the Wind: Complete Davrin's first quest plus Taash's Fire On the Sands before this
- A Fighting Chance: Complete Taash's A Little Dragon Hatches before this
- Blood of Arlathan: Complete Davrin's Hope on the Wing quest before this
It's likely that there are more companion quests that are locked by these events since they often unlock in order, but these are the main companion and faction ones I found. If you generally just watch out for the quests that direct you to gather everyone together in the Lighthouse, these are usually significant ones that move the main plot along.
