Function Alternative for COUNTIF()

[Gabriel_Leal]

Hey! I'm having an issue with appp sheets, I have a table on google sheets that tracks employees clock in time and clock out time, each time they clock in and clock out is a new entry. I want to make a validation rule that will only allow them to clock in again when they are clocked out, so they wouldn't be clocked in on multiple tasks at the same time. 
On google sheets I was using this formula which would tell me if they're currently clock in (=IF(COUNTIFs('PBI - Clock In Out'!B:B,A2,'PBI - Clock In Out'!K:K,"Clocked In")>0,"Yes","No"), and did a validation rule that only employees with "No" Could clock in, but it takes 5 to 10 minutes for the data to refresh so their name won't show right away. 
Appsheet don't have the COUNTIF formula and I tried this formula with the data validation (AND([Clocked In Status]= "Clocked Out",[Date]=today()-1)) which shows me Yes to those that are Clocked Out and No to those that are Clocked In, but their nome don't show up for clock in.
Any idea of what's going on? Or any idea of a formula that could substitute COUNTIF()? 

[AleksiAlkio]

Do you want to filter employee's name in the dropdown or do you want to add a validation rule so they can pick the name, but then it throws a validation error?

[Gabriel_Leal]

I want to filter their name in the dropdown, so if they are already clocked in a task, they wouldn't see their name again in the clock in form dropdown list.

[AleksiAlkio]

You could use Suggested values with a formula something like..
Users[User] - SELECT(Data[User],
AND(
ISNOTBLANK([In]),
ISBLANK([Out]),
DATE([In])=TODAY()
))

[Peterson_90]

I recommend you use COUNT(SELECT())