I'm afraid you can't. Even if you buy Explaindio Elements Agency without the Standard Version, you will not be able to use Explaindio Elements without the Standard version.
Here is why:
1. Explaindio Elements Standard Version is the main product which comes as Monthly, Annual or a Special One-Off payment subscription.
2. Explaindio Elements Agency is an Upgrade or Up-sell which gives you 5 Additional License Keys for your Explaindio Elements software and allows you to integrate your Pixabay API to get Royalty Free Images.
3. Since Explaindio Elements Agency is not independent, you will need to subscribe for the main product Explaindio Elements Monthly, Annual or a Special One-Off payment subscription. Else you can't use Explaindio Elements with only Explaindio Elements Agency in your account.