2008 iMac

Do you have access to another Mac compatible with macOS 10.11 where you can download and create a bootable macOS 10.11 El Capitan USB installer?

https://support.apple.com/en-us/HT201372

@padams35 is correct that Linux can extend the useful life of a 2008 iMac if the hard drive is still healthy and the computer has at least 4GB of memory. Linux Mint is a good choice as it should be easy to install. Linux would give you access to the current versions of popular browsers such as Firefox, Chrome, Vivaldi, etc. had has easy access to lots of free open source apps. It does require you to learn a new operating system, but for basic usage it shouldn't be too difficult with Linux Mint. IIRC you can try out a Live USB version to see what it is like keeping in mind running it from a USB stick may be slow.

It has been obsolete for many years and the applications are extremely out of date. After doing ALL of the following in What to do before selling or giving away your Mac - Apple Support then I would have Apple recycle it for you per the directions in https://www.apple.com/recycling/nationalservices/

Sure.

• They make for fancy Linux boxes.
• Great for nostalgia. Keep it around to run all your favorite 32-bit applications that won't run on a new mac with Catalina.
• Great for retro-computing. With Snow Leopard Rosetta you can run old school PowerPC applications.

El Capitan being unavailable is odd.

Which OS is currently installed? Have you tried this support article? https://support.apple.com/en-us/HT206886