Something to keep in mind is that this is about certification of products, not people. This is not a regulation for the profession of Software Developer, but a regulation for software products. The EU knows very well that it needs more people from all backgrounds writing and understanding software, not less.

As it is, I think this is going to be very similar to what is already required for some specific industries like healthcare or finance. Startups that want to operate in these industries already need to go through some certification processes of their products and services. Most startups will probably fall under the "low risk status" category until they are a big enough. If self-assessment is anything similar to what it is already required for things like PCI DSS or GDPR, then most small companies will be fine until they are big enough to care.

And by the way, there is no easy way for the EU to regulate that to write software you need a specific degree.