[epmos]

No-one else mentioned it, so I might suggest punched tape. https://en.wikipedia.org/wiki/Punched_tape

There is always a trade-off between mass, durability, and data density. I know you excluded those considerations, but for only 200 years in a time capsule you likely don't want to use large stone blocks or stainless steel.

The tape has several advantages. Mylar is very light and kept in the dark at a constant, reasonable temperature is going to last two centuries no problem. You can read the tape by hand, if you need. An 8-bit tape is an inch wide and can be rolled into a canister for your time capsule.

Of course, for small amounts of data print English words on acid-free paper. For large amounts, tape is going to blow out the mass budget you didn't know you had because of it's low data density. But there might be a space in there somewhere for a tech I loved as a kid.