It is always better to use proper objects

dynamic is a relic of the past that should be avoided in new development

for things like deserializing JSON, there are tools which can automatically generate proper DTO types

As a rule of thumb:
Never ever ever ever ever ever ever ever use dynamic

Yeah thought so.. got some old project of a coworker, and there is lots of dynamic/object usage, which I honestly didnt rly use before..

Is there any big difference between those, or are they kinda the same? (object/dynamic)

using object is slightly better

but only slightly

dynamic completely turns off all form of type-checking during compilation

with object, you can at least use 'is' checks to try and be a bit safer

it's still not preferable, though - if you have a method that takes object as an argument, it is usually possible to make it generic instead

in case you didn't know, object is what everything in .NET inherits from. so it's still in the type-system, just so vague and abstract it's hard to do anything useful with it safely

I saw one usage of dynamic in production code, and it was to do:

void SomeMethod(MyOneObject x) => ...;
void SomeMethod(MyOtherObject x) => ...;
void SomeMethod(SomeWeirdObject x) => ...;

void GenericMethod<T>
{
    T obj = ...;
    SomeMethod((dynamic) obj);
}

that worries me

Especially when it comes to readibility, you have to search a lot of parts of the code before you even know what you are working with..
and when you use same code for multiple object types and suddenly random exceptions are coming to the fore

yyyyyep

such is life with legacy codebases

I think that's like one of the only actually acceptable-ish uses of it

acceptable-ish, yeah

still gives you runtime errors if no overload is found I think

I think it'll pick the most specific overload