Well inside the tank the screws need rubber washers to prevent leakage from the holes. Bottom with the nut has a washer like that and screw. Washer to protect the tank integrity. They crack easily.

Idk what the pieces are, can't get the images to load.

Feedback for future projects: if you take pics while disassembling something, you'll have a handy reference for putting it back together.

The picture of the pieces have been updated in the post.

Yeah… I totally forgot. Truth is, I didn’t think anything would wrong 😅

As you found them on the floor and one of them looks like a spacer (tube shape), I wouldnt be surprised if these dropped off when you removed the screws holding the cistern to the wall. Do you have rawplugs in the wall still from where the cistern was attached? If so, have the screws you took out of them got rubber washers on them?

My guess is they belong to the screws that attach the tank to the base.

This is a conventional two piece toilet. No wall-mount whatsoever. Upper tank to base uses two bolts, two nuts, two spongy big fat washers twixt the two porcelain parts , two harder washers under the nuts and sometimes one or two spacers to prevent tilt as well as one Very Big Spongy Washer that does the actual water seal twist tank and base.

Prepare for a leaky wc

Ours is pretty much the same, just has the wall mount too. Might be a UK thing.