Question on Smart Thermostat Wiring

https://shanekfrx461.zenbloomer.com/posts/signs-your-ac-needs-repair-in-north-fort-worth-before-you-call-comfort-experts-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