Is it possible to turn off the tax for a client who is a non-UK resident?
There is no mechanism for simply switching off taxation in the UK version of Voyant Adviser. It is setup with UK tax rules and not designed as a multi-jurisdictional tool. That said, if you were to enter investments as Type: Offshore Taxable (with the tax rate set to zero), and use Other Income (non-taxable), instead of Employment, to record your client's income, you could effectively eschew most UK taxes. The remaining tax consideration, which cannot be eschewed, is the end-of-life/end-of-plan IHT tax calculations. Those taxes however don't generally affect the calculation of the plan's cash flow over the life of the plan.