We made some changes to the low-level method call ABI in 10.3, which affects both Delphi and C++. This is likely to be invisible to you unless you do something very low-level. It's more visible to you if you use C++, because now an entire class of bugs has been fixed in one go.
IMO, whether you use C++ or not, it's very interesting!
Info here: https://community.idera.com/developer-tools/b/blog/posts/abi-changes-in-rad-studio-10-3