Entering Thailand is becoming easier and easier. As a tourist you don’t need a visa, you can travel freely in Thailand for 30 days without any problems. The government is currently discussing extending this to 90 days.
If you want to settle in Thailand for a longer period of time and live here, for example as a retirement home, you simply apply for a non-immigrant E-Visa for 90 days in your home country (D-A-CH). https://thaievisa.go.th
After entry, this 90-day visa can be converted into a one-year residence permit (proof of residence and 800,000 Thai Baht in a Thai bank), which is extended every year.
You only need proof of health insurance with coverage of 100 K USD if you apply for the annual visa directly in your home country using the e-visa.