If the iMac is a 2013 model, it is either a 21.5" or 27" Mac. The last 24" iMac, prior to the 2021 release, was the 2009 model.
The 2013 iMac can run macOS 10.15.7 but nothing newer. The machine is still very capable of productive use, but each passing year brings it closer to the dust bin as security updates and other software and hardware support have evaporated.
I continue to use my 2013 iMac as a media (music and movies) server at home. I can still access my credit union and most other websites as needed, though sometimes this means I launch Firefox rather than Safari because that app is still updated by its developers. The installed office apps still run fine and music production happens though with a slightly older version of Logic Pro is current. But I know it won't be long now before the 2013 iMac gets the boot.
Ten years is a good run for any computer. How you "up-cycle?" your Mac is up to you. Sometimes the best you can do with old tech is wipe the drive, reinstall a fresh copy of the newest OS it can run and then maybe sell it for a few $$, pay it forward by giving it away to someone who can appreciate the limitations of a vintage machine, or simply turn it in for recycling.