Proton Pass will only import login, note and card items from Bitwarden but not identity items since we don't support this item type at the moment.
We improved the Bitwarden import in https://github.com/ProtonMail/WebClients/commit/4368d029104933c314c7f7eaf15447dd3737077c: when importing from Bitwarden you will now have the option to import each Bitwarden folder into a separate Proton Pass vault. This improvement is in version 1.9.1, released some days ago on Chromium browsers and yesterday on Firefox.
I imported from Bitwarden to ProtonPass and found a couple challenges: