I can’t upgrade my iPhone 5s

Correct.

An iPhone 5S can't be updated beyond 12.5.7, it doesn't have the hardware required to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.7

• If you have an iPhone 6S through 7, or SE 1st generation, you can update to 15.8.2

• If you have an iPhone 8 or X, you can update to 16.7.10

• If you have an iPhone SE (2nd generation or later), or XR through 15, you can update to 17.6. 1

Apple released the iPhone 5s nearly 11 years ago.

It only has 1 GB of RAM.

All iPhones that can run versions of iOS more recent than iOS 12 have more RAM – anywhere from 2 GB to 8 GB – and more recent processors, as well. Almost all of the iPhones that can run iOS 17 have at least 4 GB of RAM (one or two have "only" 3 GB). The iPhone 5s is simply too outdated to run modern versions of iOS.