At the end of the day, it was a very stressful update. But with the two plugins in question, it was possible to set up DynDNS and ACME without any problems. The only thing that made it a bit more time-consuming was the fact that DynDNS is a bit cumbersome to set up under IONOS (API) because you have to generate a URL in IONOS and a domain cannot be selected on-the-fly in the plugin.