You joined as a participant for studies in general, so this applies to all of them — there is no way to leave just one.
What happens
Chat about home energy ends now — it is the one study you are currently in.
You stop receiving invitations to new studies.
You will not be added to studies that start later.
What stays
Your account, so you can sign in whenever you like.
The two studies you already finished, still readable.
Everything you wrote. Nothing is deleted.
You can rejoin later. Come back to Preferences and choose to rejoin — you will be eligible for studies that start after that. Studies that ended today will not restart.