I had this idea to create a new cryptocurrency that uses rendering as mining, using it to create a decentralized render farm. is it possible, and if yes, then how? Sorry the question is not in depth. I'll edit this as I go along. Thanks!
A proof of work is a piece of data which is difficult (costly, time-consuming) to produce but easy for others to verify. You might be able to squeeze a render job into those constraints (remember, easy to verify also means it needs to be easy (small) to download, otherwise it's already a DOS opportunity right there).
However, another PoW requirement is that the work must be progress-free, which means every iteration of the work is completely independent of all other iterations (like rolling dice). This is because if you have 10% of the capacity, you'll win 10% of the time. As soon as there is progress in the work (20% done, 50% done, 99% done ... 100% done) then the fastest render farm will win 100% of the time (defeating the whole purpose of PoW). That situation also opens up all kinds of exploits where a fast farm can work ahead on the next block and gain an even bigger advantage.
There are many aspects to being progress-free. Even the current bitcoin PoW has a little bit of progress in practice (the block propagation itself) and even a little bit causes centralization pressure: bigger farms have a slight advantage over smaller farms.