I’ve been pondering this for a few days.
When I was a child there were two priests who were very close to my family. One was our Pastor, a grandfatherly type who’d been Pastor in my village for over 30 years. He was Dad’s best friend and Dad never called him anything but Fr. Surname. Same with the Redemptorist who visited each year.
The only priests I knew who were called Fr. First Name were the two who had grown up in our village, one was Dad’s cousin so of course he was Fr. Henri, and the other was a much younger man who became Fr. Armand.
But the times were very different. Our parents’ close friends were all Mr. & Mrs. First Name. Those who had a closer relationship to the family than that were Uncle and Aunt First Name.
As you know, in French, politeness dictates that you address strangers or adult in the second person plural, always ‘vous’ and not ‘tu’. Some of my friends were brought up to address their parents in the second person plural, something Dad pointed out to us at a young age to show us how liberal he was allowing to address him as ‘tu’.

I smile because he was soooo not liberal.
Then I grew up. I got married and never wanted to be addressed as Mrs anything. I wanted no title. Mrs X was my mother-in-law, not I. When my kids were born, I tried to have them call my friends Mr. or Mrs. Surname but nobody wanted that and even my 3 year olds were told by my friends to call them ‘Marie’ or ‘Fred’.
Now, as far as I’m concerned, politeness dictates that you call people by the name they want to be called. You don’t use a nickname with someone who doesn’t want one (my pet peeve, I want to be called by my full given name, not the shortened version, or worse, the cutesy version that I’ve avoided for the last 59 years). I’ve called three priests by their first names, no title. I worked with them and that’s how they wished to be addressed. The others I worked with, all members of a religious congregation, were called Fr. First Name. Even the Bishop, also a member of that congregation, would call the office and identify himself, “Phemie, it’s Doug.” To me he was always Bishop Doug.
Now we have a new Bishop. He’s Bishop Last Name until he indicates he wants something different. We also have a new Pastor, a diocesan priest. He identifies himself as Fr. Surname and I don’t call him anything else. My friend, whose home the Pastor has adopted as his own and where he frequently drops in unannounced, calls him Fr. First Name.