Can I install macOS Sonoma on my old iMac?

Your tag line says that you have an "iMac Pro (2017)", but your post says that your iMac is running Mavericks. The iMac Pro originally shipped with macOS 10.13.2 (High Sierra) - so whatever your "old iMac" is, it is not an iMac Pro.

According to MacTracker,

• The most recent 21.5" iMac that could run Mavericks was the Mid 2014 one. For it, Big Sur is the end of the line.
• The most recent 27" iMac that could run Mavericks was the Late 2013 one. For it, Catalina is the end of the line.

The end of the line for your iMac will depend on its specific model and hardware year, which you can find by looking in the About This Mac dialog in the Apple () menu. But it's clear from the information that you have supplied that your iMac is not able to run one of "the most recent three" (Monterey, Ventura, Sonoma).

FWIW, there's no way a Mac that can run Mavericks can run Sonoma. Sonoma will require one of these Macs.

Sonoma will not work with 2017 models of the iMac or MacBook Pro. In addition to take advantage of many of the new features you would still need an Apple Silicon model.

Mavericks is only compatible with some 2014 and older Macs to 2007. So clearly it isn't your iMac Pro that has Mavericks on it. Without knowing what you have with Mavericks, we can't tell you the maximum OS of your Mavericks machine.

Sonoma is supported on the 2017 iMac Pro, which is in the OP's profile. A Mac that is currently running Mavericks however is at least ten years old and excluded.