I can think of use discoveries as the things which have been found. Is there a way to do that by transforming the word found? Like we can say "things which belong to you" as "your belongings".
This depends on the context:
findings usually refers to things found through investigation:
finding n. A conclusion reached as a result of an inquiry, investigation, or trial
discoveries implies either facts that one has become aware of, things found by accident or chance, or things found as a result of a process (such as oil discovered by exploration)
Find (something or someone) unexpectedly or in the course of a search
Become aware of (a fact or situation)
discovery n. A person or thing discovered
find can be used as a noun in some contexts:
find n. (pl. finds) A discovery of something valuable, typically something of archaeological interest
None of these words would really be appropriate for things found in the normal course of life, for example I keep a shoebox of interesting things I have found on the ground out-and-about. It would not really be correct to call them my findings, nor my discoveries, things I found is probably the best word / phrase to use in this context.
For things, findings is the correct word, especially in research.
For abandoned children, the word is foundling
Try findings. The infinitive for "found" is "find", thus word "findings" is probably what you are looking for.
Miscellaneous discovered objects included in an art piece or exhibited as an art piece are known as ‘found objects’.
A found object is also known as an objet trouvé, from the French for found object.
Contemporary Collage of "found" cigarette butts, by Dan Mountford.