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Is this stopping agents running in the JVM?

No. This change only prints a warning, nothing else. There is also a proposal for a future change to the default from -XX:+EnableDynamicAgentLoading to -XX:-EnableDynamicAgentLoading (probably in Java 25)

Will the proposed future change stop agents running in the JVM?

The proposed change still allows agents to load into the JVM. If the proposed change is applied, agents will still be able to load at startup using -javaagent and -agentlib, and also after startup if -XX:+EnableDynamicAgentLoading is added to the JVM command line

Does the proposed future change enable any feature?

No. There are no features planned, proposed or even envisaged that will be enabled if the EnableDynamicAgentLoading default is changed

Okay, so does the proposed future change prevent some technical or security issues?

No. Security is not even mentioned in the JEP, and there are no actual issues related to agents loading dynamically, and no actual (as opposed to hypothetical) problems with it

So if there are no actual problems with the current default and no features will be enabled by changing it, why is it proposed to change?

The maintainers don't like the current default. There is an attempt at justifying that dislike in the JEP

Does any of this matter?

Probably not. It depends on how you look at it. Fewer than 2% of production systems will be adversely affected if the proposed future change proceeds, and 0% of deployments will actually benefit from the proposed change. No practical benefit and some adverse impact but the maintainers really really don't like the default as is. So the proposed change will likely go ahead, with some inconvenience for a minority of JVM users. In other words it matters to some people, but not to most