A psychotherapist is not universally required for psychedelic work; it depends on your legal setting and your goals.
In regulated clinical programs and for any future reimbursement, a licensed psychotherapist with specific psychedelic training is typically expected. Policies differ by country and over time, and I cannot verify the current status in the Netherlands.
Outside formal healthcare, some people use non-medical therapeutic guides with legal substances where that is allowed. If you choose this, vet the guide’s ethics and training, discuss screening, preparation, and integration, and check local laws.
For a concise take on when a psychotherapist is needed in different contexts, see this short overview.
Hope this helps.