Hi, I'm having the same issue right now. Tested it with Zabbix Agent 2 5.0.24 and 6.0.5.

I'm also having the same issue

I faced the same issue and reversed engineered the discovery for the instances discovery for our Infrastructure.

$services = Get-Service "mssql$*"|Select-Object -ExpandProperty Name
$data = foreach ($service in $services) {
    [PSCustomObject]@{
		"{#INSTANCES}" = $service
	}
}

$data|ConvertTo-Json

UserParameter=windowssqlinstances.discovery[*],powershell.exe -command "& '%programfiles%\Zabbix\scripts\windowssqlinstances.ps1'"

I don't know if the instance names always match the name of the service, as they do at my company.

side note: i had to add/change the discovery filter to a marco, like this:

{$MSSQL.MULTI.INSTANCE.MATCHAES} = ".*" for match

I faced the same issue and reversed engineered the discovery for the instances discovery for our Infrastructure.

$services = Get-Service "mssql$*"|Select-Object -ExpandProperty Name
$data = foreach ($service in $services) {
    [PSCustomObject]@{
		"{#INSTANCES}" = $service
	}
}

$data|ConvertTo-Json

UserParameter=windowssqlinstances.discovery[*],powershell.exe -command "& '%programfiles%\Zabbix\scripts\windowssqlinstances.ps1'"

I don't know if the instance names always match the name of the service, as they do at my company.

side note: i had to add/change the discovery filter to a marco, like this:

{$MSSQL.MULTI.INSTANCE.MATCHAES} = ".*" for match

I was able to reproduce / fix it the way you described

I've created a Pull Request Draft, (Only for version 6.0 and Instance)
Please @chi110r check if it is like you added.
If so i can add the other files to the PR.
And maybe afterwards we get somebody to approve it :)