HI
"Digging further, I found that the PS_BgpRouter_v1.0.cdxml file (located in C:\Windows\System32\WindowsPowerShell\v1.0\Modules\RemoteAccess) has a validater that limits the number to be no larger than 65534"
1."Are 32-bit ASNs in BGP supported by Microsoft?"
No,i also think it not support now .from above your description, i think you have found the reason. The reason is that BgpRouter_v1.0.cdxml limit the number to be no larger than 65534 and this file is older than current BGP technical requirements.
2.if we update the latest powershell version ,will the same issue happen ?
Installing PowerShell on Windows
https://learn.microsoft.com/en-us/powershell/scripting/install/installing-powershell-core-on-windows?view=powershell-7
3.I think if you use 16-bit ASNs in BGP ,it will be also compatibled with the 32-bit AS in BGP.
BGP Implementation Using 32-bit AS Number Configuration Example
https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/113593-config-bgp-using-32bit-ASN-00.html
4.Are there any additional ways to configure BGP besides PowerShell?
I haven't seen other method to configure BGP in windows platform, so powershell is only way.