Legally, joint bank accounts are an advantage so if one of the joint owners passes away, the account isn't locked and bill paying capabilities aren't disrupted. If the accounts are singly-owned, then they are subject to locking out unless/until the beneficiary/heir identity is established to the financial institution's requirements.
For most of my marriage, we had two joint accounts but one was my personal account, and one was his. We did not check up on each others' accounts, but the ability to do so was there if there was an emergency. We had them at the same bank so the login was the same, just remembered which one was which and mostly didn't worry about things other than making sure the bills were paid and there were no too low balances and the like. We each controlled our own income and paid all the bills from one or the other. After the both of us FIREd, there wasn't a real need to have two of them as there was no income streams other than the investments, so we closed one and both use a single joint account now to keep things simple and easy.
No way I'd do a joint brokerage/investment account as that would lose the stepped up cost advantage. You can make the other a fully authorized user and make sure they are the beneficiary, but the stepped up cost thing is mega important to safeguard.