Wait I'm lost... Do you mean my npub is a BTC address?
All nostr users have a native bitcoin address.
Bitcoin pubkeys and nostr pubkeys are the same address with a different prefix. You can send btc to your npub on-chain and your nsec can unlock it.
nostr:nprofile1qqsdulkdrc5hdf4dktl6taxmsxnasykghdnf32sqmnc7w6km2hhav3gppemhxue69uhkummn9ekx7mp0qywhwumn8ghj7mn0wd68ytfsxyhxymmvwshx7cnnv4e8vetj9uq3uamnwvaz7tmwdaehgu3dwp6kytnhv4kxcmmjv3jhytnwv46z7qmml2f has even explored the idea of on-chain zaps
https://gist.github.com/melvincarvalho/15f767fee8ed3e14197b322235e9fe8d
Discussion
It's would be a UTXO your nsec can unlock.