IMac needed to be replaced. Put a backup of it on Google Drive, can I resore new computer from there?

You cannot use Google Drive to restore your Mac.

Use the back up drive. Run down to Best Buy or login to Amazon and find a USB-C to USB-A adapter to connect that drive to your new Mac.

Make a Time Machine backup of your iMac using an external HD, ensure the HD is formatted correctly as APFS. You should be backing up all Macs with Time Machine, if for some reason you are not familiar with Time Machine please click Back up your Mac with Time Machine. The External Hard Disk I'd recommend that you use is the https://eshop.macsales.com/shop/owc-mercury-elite-pro

After you have your Time Machine backup then setting up the new Mac is dead easy. I've put together a guide below that is simple to follow:

When you buy a new Mac the easiest, quickest and most reliable method to migrate from the old Mac to the new Mac is to simply connect the old Mac's Time Machine External Hard Disk to the new Mac using a USB cable before you turn on the new Mac. You will likely need a USB A to USB C adapter, you can find them on Amazon for $10 or less. When you start the new Mac for the first time it will startup Setup Assistant (SA), SA will get to a point where it asks if you are migrating from another computer, select Yes  and follow the on-screen prompts and it's done! It is THAT simple.

If you have already done SA on the new computer then simply connect the Time Machine External Hard Disk using a USB cable and launch Migration Assistant (MA) which is located in Applications - Utilities - MA. Then follow the on-screen prompts. 

The ONLY difference between MA and SA is MA will create a new user account that you need to log into.

Both SA and MA migrate applications (not 32 bit apps), data files & settings. They do not migrate Mac OS itself. Some professional apps such as Adobe and Microsoft apps may require re-installing their apps as they will not allow them to be migrated. As long as you kept the security keys for installing their apps, it is not an issue. 

Finally, never EVER use Wi-Fi when doing Setup Assistant or Migration Assistant. Why, it simply fails in most cases. Please read and follow the directions in Setup Assistant and Migration Assistant. If you do not have a Time Machine backup of the older Mac then create one! If you are not aware of Time Machine, please read Back up your Mac with Time Machine and finally if you need an External Hard Disk to use as a Time Machine External Hard Disk then many experience users on these forums prefer the OWC Mercury Elite Pro due to it's reasonable price, high level of quality and ease of use. 

Yes, you should be able to restore your new iMac from the backup stored on Google Drive. However, the process may vary depending on the backup method you used and the specific backup files you have.

If you used Time Machine to create a backup of your old iMac and stored it on Google Drive, you can restore your new iMac using the Time Machine backup. Here's how you can do it:

1. Set up your new iMac and connect it to the internet.

2. During the initial setup process, you should see an option to restore from a Time Machine backup. Choose this option.

3. Follow the on-screen instructions to sign in to your Google Drive account and locate the Time Machine backup file.

4. Once you've located the backup file, proceed with the restoration process. Your new iMac will begin restoring from the backup stored on Google Drive.

Alternatively, if you have individual files or data backups stored on Google Drive, you can manually download and transfer them to your new iMac. This may involve downloading specific files or data from Google Drive and transferring them to your new iMac using a USB drive, external hard drive, or other methods.

Regardless of the method you choose, make sure to carefully follow the instructions provided by Apple and Google Drive to ensure a successful restoration process. If you encounter any issues or have specific questions, you may want to consult Apple Support or Google Support for further assistance.