Much of the donated weapons to Ukraine from EU countries is American military hardware.
It could hardly be otherwise; NATO is obsessed (for obvious logistical reasons) with standardisation, and the US defence industry has leveraged that to become the major suppliers of hardware to all NATO member states.
There are some big EU military hardware manufacturers, of course - but in those cases, the US is often a buyer of their products, for the exact same standardisation reasons. Typically these technologies fulfil niche roles where an EU manufacturer has a qualitative advantage over similar US products, or has established a near monopoly in NATO that has resisted US encroachment on their speciality.
The following pdf is a little dated (and pre-dates the Ukraine war), but goes into this relationship in more detail on a country-by-country basis, focussing on the US defence relationship with five 'friendly' countries - France, Germany, Italy, the UK, and Sweden:
https://www.iris-france.org/wp-content/uploads/2017/09/Ares-20-Report-EU-DTIB-Sept-2017.pdf
The reliance of EU countries on US military hardware was firmly established (with France as the outlier, who retains the least dependency on US systems, despite home-grown French systems being more expensive), long before the idea of assisting Ukraine against Russian expansionism was even a thing.
Denmark is donating US weapons systems to Ukraine, not because they are US systems, so much as because US systems
are Danish systems - they are what Denmark has got.