If you want to make a string of values in Power BI, you can use the formula like this. It will join all the values, which correspond to the condition, in one line.

I advise you to use Measure for this instead of new columns.

Topics = 
VAR __DISTINCT_VALUES_COUNT = DISTINCTCOUNT('MarketTable5'[Topic])
VAR __MAX_VALUES_TO_SHOW = 500
RETURN
	CONCATENATEX(
	FILTER(VALUES('MarketTable5'[Topic]), 'MarketTable5'[Topic] <> ""),
		'MarketTable5'[Topic],
		", ",
		'MarketTable5'[Topic],
		ASC
	)

You can insert this measure into the Visual 'Card' and apply filters.