Ok, I understand better now.
1. If you have information to add to WordPress Users, then you need to use User Fields.
2. If you have Posts, you need to use Post Fields.
My reference to mimicking users to posts as outlined here is only if you want to have a Custom Search on the Front End for WordPress users, something that is not possible.
In those cases, you would follow the above DOC and create Posts that mimic the users.
https://toolset.com/documentation/user-guides/how-to-create-custom-searches-and-relationships-for-users/
I don't think you need it.
About MemberPress or LearnDash - I am not familiar with them anymore, but I have played with LearnDash and Toolset in the past and concluded that:
- you can use both software on the same install, but leave each do "it's thing" (Do not add, control, manipulate elements of Plugin A with Plugin B)
- Plugins like LearnDash or Sensei, etc., bring a lot of their controls which Toolset brings as well, which will end in conflicts or limitations if you start controlling one with another, or add data from one to another.
(Access, Post Types, Taxonomies (sometimes masked as "permissions"), forms, users, user data, user permissions, etc.).
I do understand the process that LearnDash and MemberPress provide and you describe, the thing is, those answers given by the users, should probably not be added or controlled by Toolset.
Instead, you should use LearnDash's features only to control and manipulate all it's things, like courses and permissions and data.
Even if those Fields (Answers of the "user) would be created by Toolset, I am not sure where LearnDash stores that data.
Sometimes plugins do exactly what we suggest in the above-linked document (Mimic users to posts)
So you would then need to add Posts fields if you want to enrich those data sets.
You could find out from the LearnDash Support exactly where they store the data you want to play with.
Then, depending on whether that is User Data or Post Data, you can easily A) Add fields (Either user or Post fields) and B) they will then appear where you add/edit that data)
There is one caveat here if the Plugin stores User data but shows the data to edit as Post Data in the backend, or even creates a "fake" user profile edit page, you may not see the Toolset Fields on those edit screens
As said, those plugins are quite powerful, they add a lot to the blogging software WordPress, and sometimes you may not be able to control with other plugins what they do or add.
I am not sure what you refer to by "since I can restrict what the user sees by clicking the "current logged-in user" option".
The toolset has no such option, and I would not suggest controlling LearnDash things with Toolset Access, it is generally not recommended:
https://toolset.com/home/compatibility-toolset-plugins-themes/ > Access – Control What Users Can Do
Concluding, you can use both software parallel on the same system, but try not to mix them.