Unfortunately, that is a loaded question.
The Time Capsule was a unique product.......a WiFi router with a built in hard drive designed to store Time Machine backups of your Mac(s). Another way to say the same thing.......the Time Capsule was really two products in one.
No other manufacturer ever offered a similar product, so there really is not a "replacement" for the Time Capsule.
If you don't really need another WiFi router, the simplest, cheapest and most reliable way to back up your Mac(s) is connect a USB hard drive directly to the Mac and back up that way.
Another option if you don't need another router........add a Network Attached Storage device, known as a NAS and connect that to your WiFi router to store backups from the Mac(s). The downside.......this is a far more expensive solution. NAS products from Synology are popular with Apple users.
If you really do need another router......two manufacturers.......Synology and Asus......offer WiFi routers with a USB port on the back of the product to which you can add a separate USB hard drive drive and back up that way. So, instead of an "all in one" product like the Time Capsule, you will have two separate products to provide the same service as a Time Capsule.