Nsec.app only exports nsec in encrypted form, Amethyst supports it, not sure about others. I'd suggest creating keys elsewhere, i.e. in nak.nostr.com and then importing into nsec.app if you need the raw nsec.

I have been publishing using Habla news and nsec.app just fine. Are you on iOS? Which browser? Anything related to 'blocked popups' etc when you tried to post?