We have plenty of proof of the US spying on allies in spite of those being secret foreign intelligence operations, there is afaik none whatsoever of say the Germans, the Belgians or the French doing something similar to the US.
Spying is intelligence collection. There many ways to collect intelligence. Some completely innocuous like going to a defense trade show and taking pictures. Or using satellites to capture imagery of sensitive locations or developments [1]. Military attaches at embassies who observe their host country’s military developments and operations [2]. These are capabilities that every developed nation has access to. For them not to use it puts them at a disadvantage.
You don’t think the French would love to have known about AUKUS submarine deal before it was made? It’s detrimental to not attempt to spy. The French were blindsided and I’m sure they don’t want to be blindsided again.
Establishing mere capability is pretty trivial: they have diplomats in the United States who can talk to people.