Some examples of objective truth:
The time is 7:00 PM in Chicago at the time of my writing this.
Paris is the capital of France.
JFK was assassinated in 1963.
A piece cannot be taken on the first move in a game of chess.
Sherlock Holmes lived on 221B Baker Street.
Snow is white.
The time was only 7 PM because we defined it as such. There is nothing objective about that - merely conventional.
Saying that "a pitch in baseball that bounces on the way to home plate is a ball" is objective truth is ridiculous.
It is a rule in a game we made.
All of your examples are of this type, merely conventionalized systems that most or all people would agree on, because they are conventional. That doesn't make them objective.
Objective = conventional?
That is silly.
What if I make a sandwich with the mustard on the outside of the bread. I have broken convention, but have I destroyed objective reality? Of course not.
What if my friends and I play chess with different rules?
Are we breaking objective reality?
What if someone argues that France really has two capitals when it comes to fashion, and three when it comes to wine, and several when it comes to food?
What if someone uses the Chinese calendar to describe when JFK was killed?
You might want to say that I am using language "illegally", so that what I am talking about is not really "playing chess", or not the real capital of France.
But this is just appealing to conventional uses of words. Again, conventionality.
It also requires that I understand and accept your definitions of each word you used.
But I don't, and I am willing to bet that you would have a great deal of difficulty defining a good many without appealing to the notion of convention.
Your argument against this seems to be to state that, if I disagreed with X I would be totally wrong.
Weak argument, I would say. Different interpretations will arise, without anyone necessarily being "wrong". Someone must be elected or appointed to determine what counts as "right" and "wrong", but this does not bear any relevance to objective truth.
As you mentioned, Sherlock Holmes was fictional. He didn't live anywhere.
Also, in American English, we cannot say that he lived "on" such and such, unless he actually lived on top of the building.
Is the word "on" included in your so-called objective truth?
If so, it doesn't work for hundreds of millions of people.
If not, which words are included? Who decides?
Are only the ideas to which the words point included?
What if your conceptualization of the ideas differs from mine? Whose should we use?
What if I have a more fleshed-out conceptualization of Paris, since I have been there, but yours is more abstract?
What if someone thinks about "Paris" as representing the geographical entity one time, but the voting population another time, the fashion world another time? This is not some trick of semantics, but something people actually do all the time. For example, the following sentences are really very normal, but each selects a different entity to refer to with the name "Paris":
‘Paris is a beautiful city’ (location) vs.
‘Paris set a curfew’ (government) vs.
‘Paris elected the Green candidate as mayor’ (population)
I do not consider anything you wrote to be (or represent) objective truth.
I also do not believe in objective truth.