Firstly, let's get onto the real problem that is discussed at lengths in the comments; this is a terrible idea.
The fact you want to create a table for an exact point in time smells very strongly of an XY Problem. What is the real problem you are trying to solve with this? Most likely what you really want is a partitioned table or a temporal table, so that you can query the data for an exact point in time. Which you need, we don't know, but I would suggest that you rethink your "solution" here.
As for the problem, it's working exactly as intended. Let's look at your REPLACE in solitude:
replace(convert(varchar(10), getdate(),121),'''-''','''')
So, in the above, you want to replace '-' (a hyphen wrapped in single quotes) with '' (2 single quotes). You don't want to replace a hyphen (-) with a zero length string; that would be REPLACE(..., '-','').
The style you are using, 121 gives the format yyyy-mm-dd hh:mi:ss.mmm, which doesn't contain a single single quote ('), so no wonder it isn't finding the pattern.
Though you don't need REPLACE on that date at all. YOu are taking the first 10 characters or the style and then removing the hyphens (-) to get yyyyMMdd, but there is already a style for that; style 112.
The above could be rewritten as:
DECLARE @Tabela sysname;
DECLARE @query nvarchar(max);
SET @Tabela = N'_#tmp_tt2_POS_racuni_';
SET @query = N'SELECT * INTO dbo.'+QUOTENAME(CONCAT(@Tabela,CONVERT(nvarchar(8),GETDATE(),112),,N'-'.REPLACE(CONVERT(nvarchar(10),GETDATE(),108),':',''),N'',N'NP')+N' FROM dbo._tabels;'
PRINT @query;
_#tmp_tt2_POS_racuni_isn't going to be temporary like it's name implies either. A temporary table's name must begin with a has (#); yours starts with an underscore (_). It seems both (read all?) your table (object) names do. I hope not.REPLACEfunction is working, there's just nothing to replace. Style121returns avarcharin the formatyyyy-mm-dd hh:mi:ss.mmm, and you want to replace the value'-'with''. There are no'-'patterns in your string. You actually should be replacing just-with a zero length string.112(yyyymmdd); then you don't need to use the first 10 characters of style121(yyyy-mm-dd hh:mi:ss.mmm) and remove the hyphens (-).