Is the inability to pronounce the letter "raa," which causes shyness, isolation, and prevents one from entering Quran memorization schools, predestined by Allah and a trial, and will its owner be rewarded for it?

Everything that occurs in the universe is by Allah's decree. A servant is rewarded for patience in the face of calamities, as Allah Almighty says: "Indeed, the patient will be given their reward without reckoning." This trial may elevate your ranks and expiate your sins. Deal with the matter realistically: if the defect can be remedied, then do so; otherwise, join Qur'an memorization schools, and there is no sin upon you. You will become accustomed to interacting with people, and all of Allah's creation is good, and whatever He decrees for the believer is good. Many live with similar conditions without being prevented from leading normal lives. Deal with the matter with patience and contentment with Allah's decree.