Question on Smart Thermostat Wiring

https://edwindcya012.clearminster.com/posts/short-cycling-ac-repair-explained-for-north-fort-worth-homes-by-the-comfort-experts-team

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