After updating Elastic to version 8.17, and having updated all integrations and Elastic Agents, I noticed that I get several Critical deprecation issues related to the change to use index.mapping.source.mode.
Having looked into it, it seems that some of the templates introduced via the System integration, haven't been updated or at least not been released yet.
For example the template: metrics-system.process.summary, that currently still use the _source.mode