Yes, try it from nostrapp.link, turn off extension first
nostr:nprofile1qyvhwumn8ghj7un9d3shjtnndehhyapwwdhkx6tpdshszrnhwden5te0dehhxtnvdakz7qghwaehxw309aex2mrp0yhxummnw3ezucnpdejz7qpqxdtducdnjerex88gkg2qk2atsdlqsyxqaag4h05jmcpyspqt30ws5jg057 is it possible to do the "createAccount" flow on https://nsec.app/?
Discussion
Server replies with authUrl, keys are created in the aithUrl tab, tab informs the server about the npub, server replies to createAccount
Didn't work.

Turn off your extension, nostr-login lib used here doesn't override it.
But it is off. I leave it always off these days.
Strange, this is what I see when ext is off and I click Log in in top menu.

It worked after reloading the page. Maybe it was cached.
Did you announce nsec.app with NIP-89 as a handler for NIP-46 events?
I don't see it
nak req -k 31990 -t k=24133 wss://relay.nostr.band | jq
Now I did. Don't see it here though https://nostrudel.ninja/#/signin/address/create
Any obvious complaints in console on page load or when you click Log in?