I would search for services that are very likely a long time around. The first and almost only thing, that comes to mind is a AWS S3 bucket. I'm pretty sure, that S3 will be around the next decades. Nobody knows the future of Amazon, but we can assume that the data stored in S3 has enough value for enough people on this planet, that S3 will last a loooong time. I can't imagine 100 years, but if something from our time last this long, it will be S3.
Now you just find a way to pay Amazon lot's of money in advance. Maybe someone will build a company around this idea?
Now you just find a way to pay Amazon lot's of money in advance. Maybe someone will build a company around this idea?