Is Naaman really bowing or physically forced to take a bowing position (prostration) as he lowers his master into a bowing position who is leaning on him? Certainly in his heart he is not bowing but he was concerned about the physical appearance. Giving the illusion of bowing/prostration/worship
The key lies with the word leaning on. His master is too frail to low himself and requires Naaman’s assistance. As such Naaman realizes that he too is taking a bowing stance. Because otherwise he would not assume this bow.
As such Elisha is not giving approval to worship/prostration/bowing before an idol, he is allowing Naaman to assist his master and assume the prostration position given Naaman was sensitive to offending God and understood the grave offense of intentionally bowing before an idol. Naaman was not worshiping the idol Naaman was merely helping his master worship.
Naaman was not so much concerned about his posture as he was about assisting someone in worshiping an idol. To which Elisha is telling Naaman not to be concerned because his master has authority over Naaman and Naaman was not responsible for his master’s choices.