Singapore is for residents/citizens only and close to Malaysia with its strict approval. Taiwan is less strict but requires the same documentation as workcation for Sotfpower applicants regarding evidence of income, Taiwan requires just a final balance of 500k along with 3-6 months of bank statements.
Mesotherapy is a medical treatment for hair loss so it should come under the medical DTV option. You will need to show a 6 months plus treatment plan. One session each 4 months? ? you mean one session a month ? a session every 4 months will very likely lead to a rejection.
Tobias Schmiedeberg Vietnam is more strict now approving SP applicants. Jakarta, Laos, Cambodia are friendlier. Did you provide a budget e.g 40k Euros will cover e.g