Hello, JuliaHL
I realized that you are experiencing the recent hot issue:
OneDrive shared folders in Windows File Explorer appear as Internet shortcuts (.url) instead of physical folders.
We understand that this may have caused inconvenience.
-->Update<--
Microsoft has confirmed that it is a known issue and the development team has now stepped in to fix the issue, but a full fix will still take some time as synchronized patches are needed to verify cross-platform stability.
Rest assured that this issue is still in the high priority queue and that we will sync the latest updates via our official website below and service notifications.
Fixes or workarounds for recent issues with OneDrive - Microsoft Support

Additionally, foreign MVPs have received a statement from the Microsoft OneDrive product team indicating that this issue is related to the ongoing OneDrive backend migration. Unfortunately, if one user has completed the migration and another has not, syncing shared folders will not be supported perfectly. When the migration is complete, the shared folders will be restored to their original state.
For more information, you can refer to junsungE's response in the topic below. Note that it is in Korean.
Shortcut errors in OneDrive shared files Related questions - Microsoft Community

-->Current recommended actions<--
Be patient and wait for the OneDrive team to fix this issue.
-->Temporary Alternatives You Can Try<--
While you wait, you can try the following alternatives:
- You may consider downloadingfiles from shared folders by visiting OneDrive Online****in a web browser. After editing them, reuploadthem and replace the original files to sync the latest change.
- This issue is usually unique to certainMicrosoft accounts, so when you create a new Microsoft account, you can see if you can use OneDrive properly with that new account. How to create a new Microsoft account - Microsoft Support
3. Some users mentioned that they can upload the shared folder as a network drive to use shared folders as in the past.
Note: This optiondoesn't work for all usersand is for evaluation only.
For more information, see this topic: Resolve the issue of not being able to access shared files in Microsoft Community.
As a frontline support team, we collect cases and datafrom users (including you) on a daily basis. Like you, let's /span>continue to monitor this issue to learn more about how the situation is developing. I hope I have informed you of the current status of this case and thank you again for your patience and understanding during this time.
Best wishes,
Lucia Wu - MSFT | Microsoft Community Support Specialist