Welcome to the forum.
All types of electronic components have an impedance, often the AC and DC impedances are different, they can be difficult to measure/calculate, and/or they are not needed for using the component in an ordinary design.
Often with power transformers impedances are not specified at all, only the voltage/current ratings of the primary and secondary windings and operating frequency range are given. Usually that is all you need to successfully design it into a circuit.
For impedance matching transformers the impedance specs for the primary and secondary windings are essential. If you want to match a Hi-Z 50k ohm audio circuit to a Low-Z 600 ohm audio circuit you better buy a transformer that specifies 50k and 600 for the impedances.
AFAIK, percent impedance is a specification that is typically only used for large power distribution transformers. (I’ve never designed a system with them, so have no practical experience) See https://electrical-engineering-portal.com/dry-transformer-percent-impedance-definition