Can I upgrade from High Sierra on a iMac Retina 5k 27-inch 2017 with lots of available memory?

Yes, your iMac is eligible to be upgraded up to macOS Ventura. The upgrade process should not affect any of your Mac's current data or installed third-party apps.

Some things you should do BEFORE you upgrade:

• Make a full backup of your Mac. Actually, make two using different methods. You can use Time Machine and Carbon Copy Cloner for these.
• Verify that your Mac's hardware meets or exceeds the system requirements for the new operating system. Check both the total RAM and free storage capacity of your Mac's system drive.
• Verify any currently installed third-party apps you want to continue to use are compatible with macOS Ventura. Especially, apps that are critical to you. Check with the app developers for compatibility.
• Document your network settings. Especially if you use a static IP address for your Mac, or any alternate DNS server(s), other than what your ISP provides you. Upgrading requires access to the Internet so having these handy can get you back online quickly should something go amiss.

• https://support.apple.com/en-us/108382#nosof << This support article shows you what Mac models are eligible for macOS Ventura.
• https://support.apple.com/en-us/108382#nosoftwareupdate << This support article shows you the number of ways that you can upgrade your Mac.

Catalina and later do not support 32-bit applications. So if you upgrade past Mojave, any 32-bit applications that you are running now will break. You'll need to find updated versions of them, or replacements for them, or just do without. (Or keep a drive with a High Sierra or Mojave installation around, so you can dual-boot into an older OS, when you want to run a 32-bit application such as a game.)

Upgrading to Catalina or later will let you run current versions of Firefox, Chrome, LibreOffice, and the Affinity V2 applications (Photo / Designer / Publisher). Upgrading to Monterey or Ventura would also let you run applications from the likes of Microsoft and Adobe. And Ventura will be part of "the most recent three" longer than Monterey will. IMHO there is no benefit for you in upgrading to Catalina or Big Sur when you could install Ventura instead.

You may find that a printer or scanner that has drivers for your current operating system (High Sierra) doesn't have drivers for a newer one. I did! Two things that can help with this are:

• AirPrint – if your printer supports it
• VueScan (a commercial product) – if you need to salvage an old scanner

About AirPrint - Apple Support

Hi,

You can upgrade till Ventura which no affects anything on your system.