Question on Smart Thermostat Wiring

https://damienfrli670.cloudhinter.com/posts/comfort-experts-guide-to-indoor-humidity-and-ac-repair-for-north-fort-worth-summers

Question on Smart Thermostat Wiring Our older thermostat only has four wires and no C wire. The smart model I bought says it needs one. Is an adapter safe to use, or does that cause problems with the AC down the road? Trying to avoid a wiring mistake