But yeah, closed source chip makes me a little doubtful
Airgapping has been suggested numerous times on here and might be an option depending on what you're after. (if you want to store and use a lot of different coins then it would be very impractical).
I don't think there is an airgapped hardware wallet with lots of supported coins.
To answer the original question, my recommendation would probably go to either Trezor Model T or BitBox02. Though I believe the Trezor is much higher build quality and more open (no secure element).