What is your iMac? (Click the Apple icon > About This Mac )
Mechanical hard drives are the biggest bottleneck in older Macs.
If either the SSD or the HDD fails, you lose all your data. buy fusion drive for imac
Are you comfortable , or do you prefer an external plug-and-play fix? What is your budget for the upgrade?
This is the "no-tools" solution. Buy a fast external drive (like a Samsung T7 or SanDisk Extreme), plug it in, and install macOS directly onto it. What is your iMac
You actually can’t buy a brand-new Fusion Drive today. Apple discontinued them in 2021 when they transitioned to Apple Silicon.
Pure SSDs have dropped in price so much that hybrids no longer make financial sense. Are you comfortable , or do you prefer
macOS used "tiering" to keep frequently used files on the SSD. Why you shouldn't buy one now