Count Most Recent Streak

I'd recommend to create a date table with a week number, unique across all years, like 202252. Then the following code will give you the longest streak. The idea is:

• Check for each person
• what was the last week not included in a streak
• count the weeks after which all belong to the streak
• the longest streak is the maximum streak length for a single person

Longest Streak = 
// per person, calculate the latest week under 80, then counting the weeks after are the streak length
VAR _PersonsAndStreakLength =
    ADDCOLUMNS ( 
        SUMMARIZECOLUMNS (
            'Name'[NameKey]
        ),
        "@StreakLength",
        // get the weeks and their WeekOver80 flag
        VAR _WeeksAndStreaks =
            ADDCOLUMNS (
                SUMMARIZECOLUMNS ( 
                    'Date'[WeekKey]
                ),
                "@WekOver80",
                CALCULATE ( COALESCE ( [WeekOver80], 0 ) )
            )
        VAR _LastWeekWithoutStreak = MAXX ( FILTER ( _WeeksAndStreaks, [@WekOver80] = 0 ), [WeekKey] )

        VAR _StreakLength = COUNTROWS ( FILTER ( _WeeksAndStreaks, [WeekKey] > _LastWeekWithoutStreak ) )

        RETURN

        _StreakLength
    )

RETURN

MAXX ( _PersonsAndStreakLength, [@StreakLength] )

Check this file for details. Code to generate the date table in Power Query is included, if needed. The result looks like:
Longes streak top/flop 20