Yes, "but" in this sense means "only" In all the sentences from these examples here from the Longman Dictionary, you could replace it with "only." I would say that with this meaning, 'but' is used almost exclusively in written English.: but3 adverb only This is but one example of what can happen when things go badly wrong. It’s going to be difficult. Anyway, we can but try. We have relationships of many different sorts – with our children, our parents, our boss and our friends, to name but a few. https://www.ldoceonline.com/dictionary/but#:~:text=Contemporary%20English%20%7C%20LDOCE-,but,car%2C%20but%20it's%20very%20reliable.

Thanks Kimberley!

These 2 are definitely not interchangeable in all situations. When you use "but" instead of "only", it may sound fancier - like in your example. You COULD exchange them also in a more casual sentence like this one: "I would go to the game, but/only I have a lot of homework." I guess they can be interchangeable when they are used to explain an exception to a rule, but "but" should never be before the verb - like "I only have one life." You couldn't use "but" here. I hope this helps, this is a good question!