There are a few things to consider:
1. As of version 1709, Windows 10 has SMB/CIFS 1.0 disabled out-of-the-box. It can be re-enabled through the "Turn Windows features on or off" dialog.
2. Even with SMB/CIFS 1.0, the default policy is to deny clients that don't support encryption below a certain level. This can be lowered in the Network and Sharing Centre -> Advanced sharing settings -> All Networks
3. Even with both of the above, Windows 10 won't allow authentication using protocols below NTLMv2, this can be added to Win9x with the "Active Directory Client Extensions" addon from Microsoft.
4. Even with this installed, the credential pair used by Win9x to authenticate against the remote host can be unclear, so it's usually less of a headache to disable password-protected file sharing on the Win10 machine (on the same settings screen as point 2), which has the following caveat: Remote hosts can now establish SMB/CIFS sessions with your Windows 10 machine without any authentication, and although they cannot access resources by default, this still presents a security risk.
4a. Unauthenticated clients impersonate the "NT AUTHORITY\ANONYMOUS LOGON" security principal. By default, and in any sane situation, this account should have no access to anything, but in this situation, it must be added to the ACL's of files and folders you want your Win9x boxes to be able to access. The default share-level security of "Everyone: Full Access" is acceptable, since the "Everyone" principal includes Anonymous Logon.
Side note: This is a risk of adding the "Everyone" principal to file/folder security. In most cases, when you want any logged-in user to be able to access a file, you should at least use the "Authenticated Users" principal, if not "Users", as the former includes accounts that are members of "Guests", or even no groups at all.
Last thing, I don't know if WIndows 10 responds to NetBIOS name resolution broadcasts so old clients can resolve SMB names to IP addresses, so from your Win9x box, you might need to access the Win10 PC by \\ip_address\share, but YMMV, I've had it work sometimes and not others, but using IP addresses avoids this little gotcha.
This got a bit rambly, sorry, hope it helps.
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