That article is nearly a year old an in OTEL time that is ancient 
so we should really look at the latest documentation
What I would recommend is go follow the guided setup at this time
Make sure the system integration is installed
Observability -> Add Data
Host -> Open Telemetry
And Follow the instruction
The will create a Sample otel.yml and
This approach will not even flow through the APM Server Directly from the OTEL Collector to Elastic Search
Next Steps you should really Read About EDOT and the More Update to Date Blogs and Documentation
I would also recommend to upgrade to 8.18
Note so this approach does not even use APM server.. and will not going forward
Here is the latest documentation
https://www.elastic.co/docs/reference/opentelemetry/quickstart/self-managed/hosts_vm
Here are some limitations (Like CPU etc not collected on MAC at this time etc)