Can I apply for a DTV visa with income from Forex or share market trading?

Some people have used their trading and investments or rental property income as proof of business / income for workcation, use the search function in the group

If your question is about investment account for 500k instead of savings/current account, usually no. They want to see funds in an accessible account. Dependening where you apply, some applicants in London have moved funds from investment accounts days/weeks before applying and were approved. It’s a risk and you’d have to demonstrate a strong financial position and write a good cover letter about your situation. Search the group for London

That will likely be tricky unless you have a registered company.

tax proof

When you do this as a remote job for a company or clients it should be possible.