Permissions to access folders

What I would suggest is that you switch off bitlocker completely (not just unlock), and see if the issue remains - If it does not clear it's not a Bitlocker issue, if it does then Bitlocker is at least part of the cause.

I apologise for this part if it is beneath your knowledge level.

Although you are a member of the Administrators group you actually run as a standard user, and when you need to be an administrator the UAC system elevates your user status to an admin level. This system depends upon the UAC being set correctly I always recommend one below the top, which provides the correct level of security, (the whole reason for UAC), whilst not annoying you too much (yes it can be annoying but once you use it for a while it becomes second nature and it popping up unexpectedly can prevent Virus attacks and even Ransomware.

What I do with situations like yours is to add my specific username in the security TAB of the folder properties for the locations with issues, the setting of Full Control will usually cascade down the files and folders below the top layer ( you may sometimes have to manually check a box to set this in place.

Another option is with a correctly set UAC level when you try to access an administrator area you will be prompted with a "are you Sure" type message and clicking on OK here will allow you access.

If you are dealing with a situation where you may have other users ( non Administrators), whom you wish to prevent access to the files whilst unlocked the set up using UAC as described will require them to enter an active Admin level Credentials & Password before they are granted access

Rather than me write a reply of several pages I can list a few relevant Tutorials from this site that explain better than I can (including images and examples)

Firstly we need to ensure that the UAC is set to a level that will prompt any user if they need extra rights to perform an action than they currently have. The top level is I find too invasive, but the second level has a better balance for Home or small Business use ...

Setup User Access Control (UAC)
Change User Account Control (UAC) Settings in Windows 10 | Windows 10 Tutorials

Once we have the UAC working at a suitable level, we need to set the permissions for access to files in the folders. To do this you need to give your user "Full Control" access to the various folders that you cannot at present access. Users need to Have basic Read/open/Navigate permissions Administrators, System, Also need "Full Control" but should not need changing

Basic setting of Permissions
Change Permissions of Objects for Users and Groups in Windows 10 | Windows 10 Tutorials

The permissions set above should automatically "cascade" down the folder tree to any subfolders (and thus their files), but, in systems which have issues with permissions, this is not always the case and so you could perform the "cascade" manually. If the folders are on a drive that has been used with other windows operating systems (previous Windows 8, Etc and the Windows 10 has been fresh installed), you may see some users that are named SID..... these are remnants of previous OS users access controls and can be removed if you wish as part of this process though this is not essential.

Inherited permissions (cascade permissions from top to subfolders)
Enable or Disable Inherited Permissions for Objects in Windows | Windows 10 Tutorials

Although not something I use as a default changing ownership can enable you to get things working when all else fails.

Take ownership of files
Change Owner of File, Folder, Drive, or Registry Key in Windows 10 | Windows 10 Tutorials

If you take a look at the above tutorials and maybe set a test folder up with a few files in to get familiar with the procedures or have a look at the actual folders you are welcome to clarify any points that are not clear before you start I'm here most days during UK Daytimes but the Author of the Tutorials is based in US so is often available to answer specific questions later in the day this may be done by posting in the actual Tutorial Thread

One thing I have to advise is make sure you have a copy of the files which you are changing permissions on - just in case of an accident