"There is no kill switch."
There may not be a physical "kill switch", but there are other situations that are effectively kill switches.
Just ask the Russians how well their fleet of stolen Western made airliners are fairing without software, technical, and parts support. Those airliners certainly don't have kill switches, but lack of the support resources to maintain them has effectively bricked most of the pirate fleet.
Just ask the Ukrainians about their US made weapons after the Trump administration cut off intelligence and all military shipments while Russian invaders kill thousands of Ukrainian civilians and soldiers on their homeland. The Ukrainians are fighting for their survival and the Trump administration has hamstrung them by cutting off intelligence support and resupply while Russian missiles and shells are exploding in their streets. There is not a kill switch on any of the tanks or artillery, but the withholding of the intelligence to most effectively use them and cutting off resupply is effectively a kill switch.
"The USA are still member of NATO also." Trump has repeatedly said is going to take the US out of NATO and made many decisions that are the opposite of what would be in NATO's best interests. The Europeans are taking this seriously enough to be considering forming a new organization to succeed the Five Eyes intelligence alliance without the US.
F-35s may not have actual kill switches, but there are other ways they could be bricked. Having observed the disturbing and erratic change of US leadership in January 2025, I would think any F-35 customer would have to wonder about how reliable after purchase support would be after watching the Ukrainians getting rug pulled in the middle of fighting for their survival.