There's an article with links and details on how to get other versions
macOS your Mac may (or not) be able to run. ~ With a link to latest
Big Sur, also in same article, too.
• How to get old versions of macOS - Apple Support
https://support.apple.com/en-us/HT211683
If you use any older peripherals that may not have newer drivers or
need 32-bit software, (such as printer/scanner, or other) ~ you may
consider upgrade only to Mojave 10.14.6. Be sure that your Mac is
able to run later macOS. ~ Yours may need 'hardware upgrade' too.
A hardware upgrade may mean yours could need more RAM, &/or
larger capacity hard drive, etc. An upgrade page at OWC is helpful.
Your Late 2012 27-inch iMac could use RAM upgrade in match pairs
in configurations to 16GB or 32GB. (Base HDD 1TB, 7200-RPM) with
larger options available when shipped; or later w/ service upgrade.
Catalina macOS 10.15. and Big Sur macOS 11.x run 64-bit apps only.
Earlier macOS could run both 32-bit and 64-bit. Learn what this is.
• Go 64 - Check your Apps & Prepare for a 64-bit World - stclairsoft
https://www.stclairsoft.com/Go64/index.html
"..A fast, free way to get comprehensive look at your 64-bit app
compatibility & avoid surprises before installing macOS Catalina."
Anyway, there's a ton of stuff online; & I need to go offline now..
Good luck & happy computing!
🌞🌿⛵️🌤🎣🤖🏕🐝⛄️🌻
