I saw Deezy generating me an onchain address, that looked almost exactly same (except for prefix and last 5 characters) like my nostr npub... while i only logged with Alby and they couldn't see my nsec..

itsTomekK

b86bdbc13deb52eb1172e7b2c9821b362r83973efc37cf2ee1cd56ceabdafda8b

 to convert the hex private key into bech32 encoded private key 

bitcoin_beginners

Full list of Bitcoin address prefixes

italiansatoshi

Don't think so.
You can generate a private key with:

`openssl rand -hex 32 > hexprivatekey.txt`

Example output to text file:
`b86bdbc13deb52eb1172e7b2c9821b362r83973efc37cf2ee1cd56ceabdafda8b`

You can then use a tool like [key-convertr](https://github.com/rot13maxi/key-convertr) to convert the hex private key into bech32 encoded private key `nsec....`, if needed.

Here's a [more detailed](https://orangepill.dev/nostr-guides/guide-nostr-key-generation-and-management/) explanation about Nostr keys.