Should I update my current computer operating system or is it time to buy a new computer?

I'm debating whether to try updating my system or is it time to just buy a new computer.

My current system:

27-inch iMac (mid-2011)

OS X Yosemite 10.10.52.7 GHz Intel Core i5

1TB SATA (with 397 GB available)

Two 2-GBs of 1333 MHz DDR3

AMD Radeon HD 6770M 512 MB

I cannot download current software because they need system requirements that I don't have. Today's issue was with a couple of personal finance software companies. I'm also concerned that an old computer system wouldn't be as secure as a newer one.

Does it make sense to update the operating system of is it time to just buy a new computer?

I would still use this computer for my husband's Zoom calls, checking email, etc.

Thanks for your opinions.