Umlaut domains are domains with names that contain umlauts or special characters such as ä, ö, ü, etc.
Domain names are mainly based on international spellings, and these characters were not originally intended to be used. For this reason, even today domain names which could use umlauts such as Ä, Ö, Ü are commonly spelt ae, oe, or ue instead.
More recently, umlauts can be used for domain names since all current browsers automatically convert the umlauts to ae, oe and ue, depending on the country's language.
You can use any IONOS domain as an umlaut domain. No special adjustments are necessary. Simply use the appropriate umlauts in the domain name when registering it. If the domain name is available, the domain is registered as an umlaut domain without additional costs.