Taxability

It is not the whole account profit that is taxed, but the gains on assets you sell and remit into Thailand. For example, if you sell shares for a gain and remit the proceeds, the gain portion is taxable in Thailand. Accurate records of cumulative gains are essential for compliance.

Yes, Thailand is a remittance tax basis, so you are liable for tax on the capital gains, if they are remitted / transferred into Thailand. If they are not transferred to Thailand, they are not a taxable income source.

Thailand is a remittance tax basis (so its taxable if its sent to Thailand). If the investments are transferred to Thailand then this is an assessable income source and taxable on the capital gains.