To preface, I'm not particularly knowledgeable about linguistics, but I did take several semesters of French and Spanish in college several years ago. I remember putting a lot of effort into learning how to pronounce the 'R' sound correctly in both languages.
Recently, I experimented with pronouncing different English sounds and noticed how the positioning of my tongue affects the sound produced. This led me to revisit the differences and similarities between the French and Spanish 'R' sounds. From my understanding, the Spanish 'R' is pronounced with the tongue flat and relaxed, vibrating due to airflow. The French 'R' is also made by vibrating the tongue via constricted airflow, but in the back of the throat, resulting in a more guttural sound. I can make both sounds fairly easily thanks to muscle memory from all the previous practice with both versions kicking in. And yet, they both sound and feel quite similar to me. Indeed, it seems like all that's needed to change from the Spanish pronunciation to the French is to somewhat bend the front of my tongue downward so the airflow mainly hits the back of my tongue. (Assuming I'm doing it correctly anyway. I had confirmed with my language instructors that my pronunciation of the R in each case was reasonable, if imperfect, back when I was taking those courses, but I don't currently have anyone to check with.)
Despite this, I found conflicting opinions online about their similarity. Some suggest the Spanish 'R' can substitute for the French 'R' if the guttural version is difficult, especially in singing, while others claim the sounds are very different and substituting them can cause confusion.
So now I'm curious about how professional linguists categorize the Spanish and French 'R' sounds and how similar these sounds are considered in a linguistic context. Any insights or explanations would be greatly appreciated.