Never guess your model number. Go to to find the technical model string (e.g., SM-G991U instead of just "Galaxy S21"). 2. Check the Binary Version
If you decide to use A2ZROM:
a2zrom.com is a website that distributes firmware files for many Android devices, including Samsung phones and tablets. It’s one of several third‑party archives people use to download stock ROMs, PIT files, CSC packages, and related flashable files when they need to restore, unbrick, or change the software on a Samsung device. a2zrom com samsung firmware