Question on Smart Thermostat Wiring

https://troyjueb960.publishlane.com/posts/storm-and-power-outage-advice-from-comfort-experts-for-ac-repair-in-north-fort-worth-neighborhoods-4

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