how many years Apple will support my iMac?

Using recent historical data [Catalina - Sonoma] suggests 8+ years of software updates.

5-7 years of major OS version updates from date model first sold (for models sold for less than 3 years).

2-4 years of major OS version updates from date model discontinued (for models that sold for 3+ years).

+1 year of minor point release updates,

+2 years of security updates.

Reminder: Past performance is not a guarantee of future results.

Typically 8 years for OS upgrades and around 10 for hardware repairs. It can of course be used beyond that assuming your needs are mostly static and your usage isn’t too heavy.

While Apple generally doesn't make "forward / predictive" announcements, OS history IS always available.

You can form your own predictions based on that history

While completely unofficial ... you can view the past history for OSs here:

(Caveat: I've not QA'd any of the data)

https://endoflife.date/macos

See Obtaining service for your Apple product after an expired warranty - Apple Support

Hi,

If your iMac is Apple Silicon based, your iMac would be supported more longer than intel based iMac, I suppose, though nobody here doesn't know exactly years except Apple Guys.

👍