There's this blog post about it, but it doesn't say anything about what will happen to SimpleX. SimpleX will need to comply with local law, as do all companies, but I am unsure of whether or not SimpleX Ltd. is within jurisdiction, as I believe they are based in the UK (which is no longer part of the EU after Brexit). They would, however, need to enforce the law when serving users in the jurisdiction of the EU regardless of if the law were to pass. I'm unsure how SimpleX would choose to handle that (probably just IP-based blocking, as I highly doubt they would consent to scanning), in which case your best bet is a VPN.
With chat control in the UK, there was an exception that applied to SimpleX, so unless the final law is passed, we won't know if the same would be true for the new EU law. Since servers can be self-hosted, you would likely see unofficial instances pop up that are in unaffected countries if main instances went down, but they would also be legally required to comply with the EU law when servicing EU users (though they might be less likely to do so).
I'd like an official response for clarification, but as far as the law is concerned, there's not much SimpleX can do.