I would like to prepare to ISTQB Advanced Level Test Automation Engineer exam. I am looking for potentially good quality and informative material. I just found offline tranings in training centres, but nothing about printed or online materials.
ISTQB AL TAE is very new certificate, all training centres are still working on creation of materials. Which is long and expensive process. I guess free materials you can start to expect to be available in 2-3 years.
If you cannot wait so long and cannot pay money for offline training, then the best way to prepare yourself for exam is by going through the syllabus. You will find it on the page you linked in your question: https://astqb.org/certifications/test-automation-engineer-certification/ look for pdf ISTQB Advanced Test Automation Engineer Certification Syllabus.