Does Jexo have some demo environment to access and try the Octo app?

You can create your own test environment by creating a free Jira instance Software.  Afterward creating the free Jira instance, you can install Octo from the Atlassian Marketplace.

Both Jira Software and Octo are free for up to 10 users, so you can invite 9 other colleagues to try Octo for as long as you need.

For more info, Get started with Atlassian cloud for free, Octo - Component versions, Subcomponents and Sync for Jira.