New iMac or upgrade to Big Sur

An upgraded OS may allow you to update some apps to a more recent version, but these days many developers are following Apple's lead and only supporting the most recently released OS and the two previous versions which at this time are Sonoma, Ventura, and Monterey......within a couple of months this will change to Sequoia, Sonoma, and Ventura when the next OS is released. Maybe you would have access to some new OS feature, however, since you have not already upgraded to Big Sur after four years....you probably don't want/need those features.

If you are currently running macOS 10.14 Mojave or earlier, then some of your older apps may no longer function if you upgrade to macOS 10.15+ since they do not support 32 bit apps....most maintained apps were probably already 64 bit ,but that is something you would need to consider.

For a system that old, I would be worried about a hard drive failure if you have the low end model or one with a Fusion Drive.

Any performance related issues are probably due to issues with third party software, or a worn out or failing hard drive. Upgrading the OS will not solve performance issues.....in fact it usually makes them worse and more complicated to resolve.

The 2014 iMacs are all in hospice or headed there and cannot be given a new lease of life i.e. officially Apple-obsolete. Replace with new.

New. You iMac is 10 years old.

As others have posted, that Mac is nearing its end of life.

However, it costs nothing to upgrade to the latest OS that it can accept, and once you have installed that you can use the computer until you can't, knowing that you've used it to its full potential. You might surprise yourself and get another couple years of productive use.

Time for a new machine. Big Sur is already out of support.

What is lacking on your 2014 Mac?