I am sure you have read this from the Thai Embassy in Hague re STV visa ...on the stranded forums ...
SPECIAL TOURIST VISA - STV (single entry only)
This type of visa is issued to applicants who wish to enter Thailand for tourism purposes.
STV visa holders will initially be permitted to stay in Thailand up to 90 days including the quarantine period.
The extension of stay can be requested at the Immigration Bureau in Thailand up to 2 times at the maximum of 90 days per each extension.
The maximum stay in total, therefore, shall NOT exceed 270 days including the quarantine period and shall NOT exceed 30 September 2021 which is the current end date of the STV scheme.
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