Facebook's lawyers have a blog post where they claim that complying with a FISA warrant is a GDPR violation and anyone subject to FISA warrants can't truthfully claim to be GDPR compliant
IANAL, but: In the simplest case of a purely EU company, they would not be subject to US law, and providing the US with user data would certainly violate the GDPR. In the case of a purely US company, the GDPR would prohibit them from gathering data on EU citizens and sending it back to the US. The big multinationals, like Alphabet and Meta, have therefore established subsidiary companies in the EU (of course, there may be other reasons as well). In Meta's case, their subsiduary is based in Ireland. Meta-Ireland cannot provide data on EU customers to the US, without violating EU law, and anyway is not subject to US law.
There is the more general question of whether data on EU citizens can ever be stored on US servers. If it were, then Meta-USA could be subject to FISA. For that matter, they could do all sorts of other things in violation of the GDPR. This is an ongoing issue with (afaik) no resolution in sight.
This situation annoys the US government, because they don't like being told "no". It also does not make Meta (or Google, or Amazon, any other US tech giant) happy. They occasionally threaten to leave the EU. The response from the EU is: "fine, don't let the door hit you on the way out." Which they also don't like :-)