Unable to upgrade os from Catalina to newer (iMac 2019)

Have you tried interim ones?

macOS Big Sur - Technical Specifications

General Requirements

OS X 10.9 or later

4GB of memory

35.5GB available storage on macOS Sierra or later*

Some features require an Apple ID; terms apply.

Some features require a compatible internet service provider; fees may apply.

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen and choose About This Mac. These Mac models are compatible with macOS Big Sur:

MacBook (2015 or later)

MacBook Air (2013 or later)

MacBook Pro (Late 2013 or later)

Mac mini (2014 or later)

iMac (2014 or later)

iMac Pro (2017 or later)

Mac Pro (2013 or later)

Learn about compatibility and how to identify your specific Mac model

https://apps.apple.com/us/app/macos-big-sur/id1526878132?ls=1&mt=12

And caution on 10.15 or higher, to see which Apps will no longer work in 10.15 get Go64...

https://www.stclairsoft.com/Go64/

Monterey…

macOS Monterey is compatible with these computers - Apple Support

• iMac – all models from late 2015, iMac 16,1 – 20,2
• iMac Pro – all models, iMac Pro 1,1
• MacBook & MacBook Retina – all models from early 2016, MacBook 9,1 – 10,1
• MacBook Pro – all models from early 2015, MacBook Pro 12,1 – 17,1
• MacBookAir – all models from early 2015, MacBook Air 7,1 – 10,1
• Mac Mini – all models from 2014, Mac Mini 7,1 – 9,1
• Mac Pro – all models from 2013, Mac Pro 6,1 – 7,1

https://wpbeaches.com/apple-minimum-system-requirements-for-macos-monterey-12/

https://apps.apple.com/us/app/macos-monterey/id1576738294

macOS Monterey on the App Store (apple.com)

https://apps.apple.com/us/app/macos-monterey/id1576738294?mt=12

Monterey full installer.app

Why does OSX Monterey 12gb download turn … - Apple Community

The following Mac computers are supported by macOS Ventura:

MacBook (2017 and newer)

MacBook Air (2018 and newer)

MacBook Pro (2017 and newer)

Mac mini (2018 and newer)

Mac Studio (2022)

iMac (2017 and newer)

iMac Pro (2017)

Mac Pro (2019 and newer)

macOS Ventura system requirements: Can your Mac run macOS 13? (idownloadblog.com)

Visit the App Store & put this in the search bar…

macos ventura

You can install macOS Sonoma on any of these Mac models. 

If your Mac isn't compatible with macOS Sonoma, you might be able to upgrade to an earlier version of macOS instead.

MacBook Pro

Identify your MacBook Pro

• MacBook Pro (16-inch, 2023)
• MacBook Pro (14-inch, 2023)
• MacBook Pro (13-inch, M2, 2022)
• MacBook Pro (16-inch, 2021)
• MacBook Pro (14-inch, 2021)
• MacBook Pro (13-inch, M1, 2020)
• MacBook Pro (13-inch, 2020, Two Thunderbolt 3 ports)
• MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports)
• MacBook Pro (16-inch, 2019)
• MacBook Pro (13-inch, 2019, Two Thunderbolt 3 ports)
• MacBook Pro (15-inch, 2019)
• MacBook Pro (13-inch, 2019, Four Thunderbolt 3 ports)
• MacBook Pro (15-inch, 2018)
• MacBook Pro (13-inch, 2018, Four Thunderbolt 3 ports)

MacBook Air

Identify your MacBook Air

• MacBook Air (15-inch, M2, 2023)
• MacBook Air (M2, 2022)
• MacBook Air (M1, 2020)
• MacBook Air (Retina, 13-inch, 2020)
• MacBook Air (Retina, 13-inch, 2019)
• MacBook Air (Retina, 13-inch, 2018)

iMac

Identify your iMac

• iMac (24-inch, M1, 2021)
• iMac (Retina 5K, 27-inch, 2020)
• iMac (Retina 5K, 27-inch, 2019)
• iMac (Retina 4K, 21.5-inch, 2019)

iMac Pro

Identify your iMac Pro

• iMac Pro (2017)

Mac mini

Identify your Mac mini

• Mac mini (2023)
• Mac mini (M1, 2020)
• Mac mini (2018)

Mac Studio

Identify your Mac Studio

• Mac Studio (2023)
• Mac Studio (2022)

Mac Pro

Identify your Mac Pro

• Mac Pro (2023)
• Mac Pro (2019)

https://apps.apple.com/us/app/macos-sonoma/id6450717509?mt=12

 Or... Start up from macOS Recovery

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

In Disk Utility>View, select Show all Devices, highlight the top left entry.

Run Disk First Aid on all items in the left panel, from top down.