It depends on your country, some require personal information and some doesn't... For the latter you still have to provide your street address. Check ANNEX III part A of EU regulation here: https://eur-lex.europa.eu/legal-content/EN/TXT/?qid=15733125...

From looking into it a bit, it looks like each country sets the requirements by themselves. In case of Finland, requirements are documented at least at https://dvv.fi/en/european-citizens-initiative ("The organisers must collect the family name, full first names, date of birth, country of permanent residence and nationality for Finnish citizens signing statements of support."). They seem to be also collecting full address when it's not required for Finnish citizens.

I guess it depends on how the petitions work in countries?

Where I'm from you never submit your national ID number (13 digit number given to each citizen once, never changes), but you do submit the "number" of your national ID (9 numbers and letters, changes when you move places or every 10 years, whichever comes first) when signing any petition.

I'm not sure, but I guess in some countries there is law against asking for certain personal information.