If you wanted to password protect certain products/collection/pages that are only for wholesale customers only, you can use an app called Locksmith. This app will allow you to hide pages from customers who do not have special access to these pages. Can you take a look at this app and see if it would work for you? There is a 15-day free trial also, so you can test it out first free of charge.
Let me know if you have any more questions, happy to help!
The app @dmwwebartisan recommended, Locksmith, is likely the best option for you here. You can use the app to hide a specific page using password protection and can then grant access to customers based on certain conditions, such as a customer tag or a passcode.