You need to answer a few questions
1. what version of moneydance were you using?
2. what type of computer? Mac or Windows? What version?
3. do you have backups of your old computer?
4. did you setup a passphrase for opening moneydance before, can you remember it?
5. can you remember your Dropbox moneydance sync passphrase?
6. Can you get any data off your old computer?
With these answers, we can provide some guidance...
If the answers to 3,5,6 are no then it gets tricky as you have no backups and no remembered encryption passphrase: if thus, then 7. can you a) if using big sur, see your iPhone in Finder, b) otherwise access / download itunes and see your iPhone in iTunes?