You have mentioned that you already have a slice set up to filter some records. It sound that you wish to now further include a condition of any random row among the filtered records. If so, you will need to combine your existing slice filter expression and the expression that selects a random value as mentioned in post by @TyAlevizos , that you have referred.
Your slice filter condition can be something like
[Key]=INDEX(SELECT(Table Name[Key], [Status] =“Open”), RANDBETWEEN (1, COUNT(SELECT(Table Name[Key], [Status]=“Open”))))
Here [Status]=“Open” is equivalent to your existing filter condition. Please replace it with the actual filter condition you have.
Basically , the combined expression selects records from the table based on your required condition and then among those selected records , the RANDBETWEEN() combined with INDEX() selects a random record.