When you log in to your Cloud Integration tenant you might see a notification like this:

Camel 3 upgrade notification
This is important if you have custom adapters installed.
The mentioned SAP Note covers important points. After completing the process I thought it would be helpful to document the high-level process step by step.
https://me.sap.com/notes/3326553
1- First you contact SAP support to create a "Camel 3 test tenant".
2- Develop your adapter to use new pom.xml Camel and ADK(adapter development kit) versions. In the code import Camel 3 classes. You can also create a new adapter project then copy your code. Just don't change scheme, metadata, or version of your adapter.
Blog post for creating a new adapter project from command line:
https://blogs.sap.com/2022/02/08/integration-suite-developing-custom-adapters-with-ide-of-your-choic...
Example pom.xml part:
<camel.version>3.14.7</camel.version>
<adk.version>2.1.1</adk.version>
Example Java imports:
import org.apache.camel.support.DefaultProducer;
import org.apache.camel.support.DefaultComponent;
Checking ID and version of the existing adapter:

currently deployed adapter on camel 2 tenant
3- When the "Camel 3" tenant is available you can run your new adapter by deploying it the regular way. Monitor -> Manage Integration Content -> Upload (+ button near search)

Uploading adapter to Camel 3 test tenant
4- Test your scenarios in Camel 3 test tenant.
5- When you are happy with the results. Now you can deploy this to your productive tenant, using "Settings"-> "Camel 3.14 Upgrade" -> Upload

Upload camel 3 adapter to existing tenant
6-Now you just need to wait until SAP automatically upgrades your tenant and deploys the new version of the adapter.

Here is a diagram for the components involved