What can I do with an old iPhone 5s?

Very little. You can use it as an iPod touch, and there are still a few apps that will work on it. A 5S does not work on any networks in the US anymore, and very few elsewhere in the world. It’s given you almost 10 years of service; it’s time to move on.

It’s still useable for lte limited bands though and doesn’t take advantage of any recent lte bands added post 2013. Like tmo using band 71 (600 mhz frequency). Also the phone doesn’t take advantage of band 66 which a lot if carriers are using for high download speeds. But other than that it’s still usable for basic things

It is totally wrong, the almost 10 years old Iphone 5s is Great, I Still Use it for Primary Phone 4G LTE