Is it possible to de-identify data so that GDPR does not apply?
Yes. If personal data is fully anonymized, it is no longer personal data, and subsequent uses of the data are no longer regulated by the GDPR.
Is it possible to fully de-anonymize data collected? Explain how.
De-anonymizing data is sometimes possible with additional information resources or unforseen techniques of data analysis or correlation synthesis.  When such techniques are discovered,  it is treated as an attack on the data of the people whose privacy is being protected. Those novel techniques are taken into account next time legal authorities consider what standards of anonymization are necessary to protect such data.