The obligations differ substantially.
Provider — you develop an AI system, or have one developed, and place it on the market or put it into service under your own name or trade mark. Heavier obligations: a risk management system, data governance, technical documentation, logging, conformity assessment and CE marking, and instructions for use.
Deployer — you use an AI system under your own authority. Lighter but real: human oversight with genuine authority to override, ensuring input data is relevant and representative, keeping logs, informing affected people, and monitoring operation.
The trap: a deployer can become a provider. Putting your own branding on a third party tool, modifying it substantially, or using it for a purpose the original provider did not intend can shift you into the heavier category. Businesses do this without realising.