Is GDPR still valid in the UK?

Yes, GDPR is still valid in the UK. Post-Brexit, it has been adopted into the domestic privacy law and termed UK GDPR. The regulation is almost word-to-word borrowed from its EU version, except that it protects the personal data of UK residents. So any organization that collects personal data of UK residents to offer them goods and services or monitor their behavior taking place in the UK must adhere to the same requirements as before.