The file manager doesn't open anymore! I can't open any folders.

I had today that same problem, but my pc is on the stable channel, even if this is a insiders´ forum I think this may be relevant/useful.
In my case it was caused by the public release on windows update of the KB5030310 update that brings copilot and the new file explorer, the file explorer was completely unusable aside from the desktop and taskbar, whenever it attempted to open any folder the explorer.exe process just crashed and restarted by itself.
After uninstalling that update the problem was solved, I would suggest reverting back the latest update if you did not try that already, then put a pause on the updates until someone at MS works on it.

Edit:

I don't know if it helps but event log shows this:

- System

- Provider

[ Name] Application Error
[ Guid] {a0e9b465-b939-57d7-b27d-95d8e925ff57}
EventID 1000
Version 0
Level 2
Task 100
Opcode 0
Keywords 0x8000000000000000
- TimeCreated

[ SystemTime] 2023-09-26T23:03:12.4177443Z
EventRecordID 90761
Correlation
- Execution

[ ProcessID] 12388
[ ThreadID] 17584
Channel Application
Computer (omitted)
- Security

[ UserID] (omitted)

- EventData

AppName explorer.exe
AppVersion 10.0.22621.2361
AppTimeStamp 480de713
ModuleName explorerframe.dll
ModuleVersion 10.0.22621.2361
ModuleTimeStamp 7b666dd1
ExceptionCode c0000005
FaultingOffset 000000000000877b
ProcessId 0x40e4
ProcessCreationTime 0x1d9f0cd9f951959
AppPath C:\WINDOWS\explorer.exe
ModulePath C:\WINDOWS\system32\explorerframe.dll
IntegratorReportId c537ffcb-eaeb-43c2-8e12-a7afb0ded4c3