if your travel with burner and normal phone for one hour, both switched on, cell tower registrations are in sync and both are easily linked. if your switch on your burner only occasionally at random locations, but cut real phone is/was there at the same time they are linkable.

to use a burner:

• never switch on at home
• leave main phone at home
• travel a reasonable distance before switching the burner on
• don’t travel with people who know you and who carry a phone
• sim & phone mustn’t be bought/topped-up in a traceable way
• cover cameras at all times (there are 0click exploits available to three letter agencies)

it’s possible, but certainly not trivial.

also: depends on the power of your adversary, as always the personal threat model is relevant. using a burner to cheat on your spouse is not the same as using one when plotting to the nuclear codes.