Max Hard Drive Size on Synology NAS
Yes, Synology are too slow on hard drive testing. It takes a long time for new capacity drives to be tested and therefore added to their compatibility lists. Normally there is no reason for bigger drives (than their spec sheets suggests) to work. When they mention a limit of 16TB, people are using 18TB and so on.
The only thing to pay attention to is XS series models. Synology allows only limited HDD models in these boxes. They want to sell their own (Toshiba relabeled) drives that are double the price and less reliable and louder than competitor drives. But they do have their own drive firmware which they say is better than firmware hard drive manufacturers have created for several decades such as Seagate health management etc.
I hope this helps