Do I need the 90 Day slip when leaving Thailand if I received a visa extension?

15th may to 31st July no need for 90 day report 🙏

If they didn't put the 90 day report slip in your passport then they probably didn't do a 90 day report. There's nothing that says a 90 day report and an extension are linked. You're still responsible for doing your 90 day report, either 90 days after you received your extension if it's your first extension, 90 days after your previous 90 day report, or 90 days after returning to Thailand from abroad. (90 days meaning 90 consecutive days inside of Thailand).

90 day report has nothing to do with leaving and the immigration at the airport could care less. If you miss a report they'll just fine you next time you need to go the immigration office.