I had a hard time trying to follow what exactly you’re trying to do here so I’ll make a few quick assumptions. I’m assuming that you don’t want to eat the whitespace after the search term.

The regex you have set up now is looking for the term “celso” and one other character that is not a single quote (‘). Because the space character is not a quote the regex matches the term and a single space – then does the replacement. If you were to set the regex to:
String regex = "";
Then you’d be matching all variations of celso without the spaces.

However if you just wanted to match the WORD “celso”, and not part of another word of a mistype (such as “celsOOOOO” which would turn into “OOOO”) you can use the word boundary regex:
String regex = "\\b";

I hope I helped.

String regex = "[^']";
String insentiveCase = "(?i)";
 
String DOCUMENTO_SAIDA = "celso foi  celso Celso CELSO";
String anotacao = "";
 String termo = "celso";
 
DOCUMENTO_SAIDA = DOCUMENTO_SAIDA.replaceAll(insentiveCase + termo + regex, anotacao);
 
System.out.println(DOCUMENTO_SAIDA);

foi CELSO

But… he eats space char after the replaced “termo”

Do you know some workaround?