Be very careful with advice given by strangers on Facebook!
I doubt very much that AirAsia will check luggage through onto a Lufthansa flight!!!
You have obviously bought two separate flights which means that you have to pass immigration to be able to get your luggage and check it in for your flight to Germany.
I don't know wether a transit visa is available, otherwise you might need a tourist visa.
Only people who plan to leave Thailand travelling to one of the very few countries which require an negative PCR test (China, India, ....?) have to have a health insurance.
Thai government will be sure that their potential treatment is covered if they test positive before departure in Thailand!
IF your onward travel goes to a country ( China, India, ....) which requests a PCR test for entry, in that case you need a health insurance because the Thai government will be certain that you can afford the possible necessary treatment if you test positive in Thailand.
All others, and that's the majority, don't need to have a health insurance.