@Taaliak
It does make sense, as it's often mentioned as a requirement. However, my understanding was that they had some flexibility, and could accept funds in a foreign account instead.
If this is the Embassy where you're making your application, and they insist on a Bulgarian account, then there isn't much option but to come here and try to open one. However, if you're in contact with them already, then try pushing back on their request, based on the difficulties of opening a personal bank account here in 2023 as a non-resident. And clarify if it must be a personal account, or if a company account (for a Bulgarian company that you own) would be acceptable.
A personal account must be opened in person, you definitely can't do it remotely, and you can't do it by proxy (attorney, etc.). When I came here, several banks were happy to open accounts just with my passport. But these days, the EU has tightened up on banks ignoring KYC/AML requirements, so most Bulgarian banks are reluctant to open accounts if you're not already a Bulgarian resident (and want a proof of address). I think some still do (maybe Postbank?), but it will just be a process of coming here as a tourist, and spending a day or two walking around town (Sofia or Plovdiv, most likely) and trying every bank branch you see. It's a headache, but I'd expect you to be successful. I've done something similar in Spain and Turkey, and it's a bit annoying (and a lot of walking), but we found a cooperative branch on the 1st day in Spain, and 2nd day in Turkey (with an introduction from a local with an account at the branch).
If you come over on Mission Bank Account then you can make the most of your trip by seeing an immigration attorney (if you're considering one), viewing some different parts of the country and/or potential properties, get a health insurance policy (one of the D visa requirements, and very easy/quick/cheap to get here), maybe finding a cheap rental (the visa also needs a proof of address, normally a long-term rental contract or the notary act of a purchased property).
A company account is a different story. And, if you plan, as a non-EU citizen, to purchase a village house, you will need one anyway. You should be able to give an attorney POA to open a Bulgarian company, and open the bank account for it (and get an official statement after you've put some money in the account).