Greetings LindaBre,
Thanks for posting in the Apple Support Communities.
Congratulations on your new iMac! We understand wanting to continue with your presentation on the go, so let's see if we can help with that.
For starters, let's have you confirm that you're signed in with the same Apple ID and iCloud information on your devices. This will be how your presentation can sync between your iMac, iPhone, and iPad. Check out the steps below to sync a presentation from your Mac, and you can find additional helpful information here: Sync a Keynote presentation across devices - Apple Support
Sync a presentation from a Mac
Make sure your Mac is set up with iCloud and has macOS 11 or later installed.
1. On your Mac, open the presentation you want to appear in iCloud.
2. Do either of the following:
• For an already saved presentation: Choose File > Move To, then click the Where pop-up menu and choose iCloud.
• For an unsaved presentation: Choose File > Save, then click the Where pop-up menu and choose iCloud.
Changes you make to the presentation in Keynote for iCloud appear automatically in Keynote on your Mac, and vice versa.
We hope that helps! Let us know if you've already taken these steps, and provide more details for understand what happens better. We'll pick up from there.
Have a great day!