nothing to do with withholding tax. All income arising in France is subject to French tax. Just as all income arising in the UK is subject to UK tax. There can be some adjustments due to Dual Tax Agreements where tax on certain types of income is paid in one country or another but I'm not aware of any that affect earned income.
that's complete nonsense. Anyone who spends 180 days or more inside Thailand in a calendar year automatically becomes a Thai tax resident in that year. Having a bank account is not relevant. Having a visa is not relevant.
How do you not pay taxes in France? All income from French sources is still taxable in France whether you are resident there or not. Additionally income you bring into Thailand (by any means, not just via a bank) in any year where you spend 180 days or more in the country is assessable for Thai tax. Thailand and France have a Dual Tax Agreement so you can claim a credit for any tax you may or may not have paid in France on the money you bring in
"No, the Privilege Entry Visa is a long-term tourist visa and does not allow for any employment or work in the Kingdom. This includes working remotely for a non-Thai business."
The website you link to is not an official website, it's an agents website. Unless you can show me something official that says you can legally work remotely I'm going to stick with what I said.