Thank you for your swift response! Sadly, I'm still not clear.
Which OneDrive account? The folder owner's account (theirs) or the share recipient's account (mine)?
Edit: Ah, never mind - my own, as I tried, should have probably worked, but it didn't for me due to my own particular setup. Since others may share it, here are the details:
After entering login credentials the dialog disappeared, made me wait and then failed without a descriptive error message. Now that I've checked my emails this morning, I can see why it failed.
For me at least, this fix depends on App Passwords - I received a few of these emails around the time of my login attempt.

App Passwords are like a semi-permanent way to work around MFA - a way to revert to username and password, but with a password individual to each service that requires it. I am uncomfortable with this, but need this temporary workaround.
In my case, with MFA enabled, it is apparent that I needed to use my own OneDrive email with an App Password generated by following the instructions in the above email (after satisfying myself it was genuine and pointing to a genuine MS link location, of course)
However, after entering these credentials with apparent success and opening the shared folder, I was then greeted with:

My plight continues.
At this point I am aware I have just generated a semi-permanent password with unfiltered access to my Microsoft Account and that can avoid Multi Factor Authentication
So I have also ensured I have a future reminder to revoke the app password as soon as this issue is fixed (or immediately if I can't actually get this workaround to work or me anyway) - it bypasses MFA and could by used by any actor to access all my Microsoft services. There is no apparent way to limit the scope of access of this App Password, to see successful or unsuccessful login attempts using them specifically, nor any way to revoke them individually - MS has removed all methods for listing active App Passwords and only offers an option to revoke all of them at once.
This means that if I previously generated an App Password to enable some service or other (in a prior incarnation of the UI, where I expected to be able to continue to see and administer each password individually), I will be breaking that when I revoke it - but I'm comfortable with that as closing such access is important to me (see background below).
It does not appear to be a particularly high entropy password either, being as it consists of only 16 lowercase letters, and I do not have any information on Microsoft's policy and practice in monitoring for unauthorised authentication attemps for App Passwords.
Background and caution:
When the removal of access to the shared files and folders on my own computer first occurred, I literally saw my files and folders being deleted before my eyes as I was working in the shared folder when it happened - you can imagine my reaction! I immediately paused OneDrive syncing and went to my Microsoft Account to see all was still secure - I feared the worst, that my system or account had been compromised.
In my login history, I was relieved to see no such compromise, but I did note that I receive unsuccessful login attempts against my account every few hours from various parts of the world. Like many, nefarious actors are constantly attempting to access my online services. For me this renders Multi Factor Authentication an absolute necessity.
I am now concerned that to access these files I have had to add an access method with significantly reduced secruity, albeit temporarily, while under persistent active attack.