How to set in SQL a Flag based on days range

Sample table (customer) have the following data,

As per below query, will get the similar customer with rowNumber(). Think the problem is the the comparison of data set with createdDate.

select
    RecID, createdDate, UserID,
    row_number() over (partition by UserID order by UserID) as "ROWNUMBER",
    toCount
from (
    select
       *,
       (case when datediff(day, lag(createdDate,50,createdDate) over (partition by UserID order by UserID), createdDate) <= 1 
             then 'true'
             else 'false' 
        end) as toCount
    from customer
) t

The problem: All users should receive a flag (count), who had not registered in the last 50 days. like this:

First, here's a query that I think gives you what you're looking for (let me know):

select RecId
     , createdDate
     , UserId
     , row_number() over (partition by UserId order by createdDate desc) as ROWNUMBER
     , case
          when datediff(day,lag(createdDate) over (partition by UserId order by createdDate),createdDate) <= 50 then 'false'
          else 'true'
       end as toCount
  from customer
order by RecId;

A couple of observations:

row_number() over (partition by UserID order by UserID) as "ROWNUMBER" UserID is not distinct and doesn't make a good candidate for the order by in this row_number function. It's good for partition, not for order by.

lag(createdDate,50,createdDate) That 50 in there is an offset, so you're asking to skip fifty rows, not 50 days.