is this a mechanic that has been forgotten about or is it jsut different now, my campaigns typically have alot of it so players can do individual task. Any ideas?

I couldn't find it in the 2024 PHB. Now I'm reading the 2024 DMG, but I can't find it there either.

Many downtime activities have been integrated into both the new PHB and DMG, but they're not referred to as "Downtime Activities" anymore

Xanathar’s still exists. Its downtime options still apply.

I think Bastions are the new take on Downtime Activities for the most part.

Quote from Xalthu >>

Xanathar’s still exists. Its downtime options still apply.

 It's also my recommendation when an activity hasn't been superseded by the new PHB or DMG (e.g., crafting)

As @The_Ace_of_Rogues mentioned, Bastions indeed includes some "benefits" similar to those downtime activities offered in the DMG and XGE.