Often the foundry wants to do this, same as density fills.
Have you asked whose responsibility this is?
A seal ring is a complex structure with usually one of every
layer and specific relations between them. So there is likely
a PCell for it. Whether it's provided to customers would
depend on whether they expect customers to do it. If it
is available it may be in a manufacturing structures
category; perhaps with bond pads, density fill or other
"non-circuit" elements (do not use TSMC myself, so no good
idea how they structure and subdivide their libraries.