This feels like a stupid question. In searching for Evernote replacement, last week I installed Joplin on my desktop. I don't recall setting up a password, but it has successfully imported notes from Evernote. Today I installed the Joplin app on my phone. Again no password setup required. I cannot find any account settings. How am I to log in so that I can synch between devices? Sorry if this is a stupid question.
Joplin is "offline first", meaning that there is no account, and each installation is completely separate from one another. If you want to sync your notes though, please check https://joplinapp.org/help/apps/sync and specifically all the different options listed in the sidebar.
You can create a free Dropbox or OneDrive (Microsoft) account if the storage limit of their free tiers is sufficient for you. Otherwise you can review paid options such as Joplin Cloud, as mentioned