I found that in our demo Microsoft 365 tenant, there were Nintex updates for Nintex Form and Nintex Workflow as shown:
Nintex Workflow for Office 365 (Version: 18.104.22.168)
Nintex Form for Office 365 (Version: 22.214.171.124)
But I got some hiccups while updating Nintex Apps for Office 365. So, let me give a step by step guide to update Nintex Apps.
Issue: Nintex Forms for Office 365 within SharePoint Online, there is no option update from SharePoint Online Store
Follow this URL (Dated: Aug 8, 2017)
Sign in your Office 365 credentials and Nintex Form will be updated.
Even after Nintex Form App update, it will still show, “An update for this app is available”.
Next, click on Nintex Form App.
This time around you will able to get the button, GET IT as shown:
Follow this URL (Dated: 29, Feb 2016)
In few minutes, Nintex Forms and Nintex Workflow Apps will be updated.
The steps may wary for different Office 365 tenants a bit, this is overall process may help you.