Do you mean unlocks, secrets, or actual Steam achievements? There haven't been any new Steam achievements in quite some time, and all of the new unlocks/secrets are related to the Castlevania DLC, so I think you may have some things from quite a while ago to do.

I'm sure folks will be happy to help, but maybe list a few of the things you are trying to do to narrow the question down.

If you mean the Secrets, the wiki has a full list; if you want to earn a specific one, click on the page it links to and there will usually be a detailed description of how to get it: https://vampire-survivors.fandom.com/wiki/Secret

Bear in mind that before you can unlock any of the Castlevania secrets, you'll first have to collect the Pile of Secrets relic.

All the steam achievements corespond to the objectives in the unlocks menu, so just look there.. Every unlock that isn't tied to one of the crossover DLCs gives an achievement.

They are mainly focused on the Darkasso. Go into the secrets page and type "forbiddenbox" to unlock the stage where you can find the Darkasso. Then there are further unlocks for each of them stated in the unlock category. Some are easy, but some require a bit of thought put in.

Theres no new hidden achievements, this topic is a trap.