It's 2025, and there's a lot of outdated docs on programming ATtiny microcontrollers (ATtiny85, ATtiny84, etc.) on Arduino.

Key things:

• You CAN do this on Arduino IDE 2.x
• The core you want is ATTinyCore. To install it:

This core can be installed using the boards manager. The boards manager URL is:
http://drazzy.com/package_drazzy.com_index.json

File→Preferences on a PC, or Arduino→Preferences on a Mac, enter the above URL in "Additional Boards Manager URLs"

Tools → Boards → Boards Manager…

Select "ATTinyCore by Spence Konde" and click "Install".