Having to make a decision isn’t my primary issue here (even though it can also be problematic, when you need to serialize domain-specific data for which you’re no expert). My issue is rather in that you have to write this decision down, so that it can be used for deserializing again. This just makes XML serialization code significantly more complex than JSON serialization code. Both in terms of the code becoming harder to understand, but also just lines of code needed.

This is, without a doubt, the stupidest argument against XML I've ever heard. Nobody has trouble with using attributes vs. tag bodies. Nobody. There are much more credible complaints to be made about parsing performance, memory overhead, extra size, complexity when using things like namespaces, etc.

I’ve somewhat come to expect less than a handful lines of code for serializing an object from memory into a file. If you do that with XML, it will just slap everything into child nodes, which may be fine, but might also not be.

No - it is fine to just use tag bodies. You don't need to ever use attributes if you don't want to. You've never actually used XML have you?

https://www.baeldung.com/jackson-xml-serialization-and-deserialization