With SQL Server you have the ability to make changes to the raw table field data within a GROUP BY clause by using a CASE statement. e.g.

SELECT [QuestionId]
      ,CASE WHEN Answer LIKE 'Other%' THEN 'Other'
			ELSE Answer END AS [Answer]
      ,count(*) as Count
  FROM [SurveyResults-Q4-2022]
  GROUP BY	QuestionId, 
		CASE WHEN Answer LIKE 'Other%' THEN 'Other'
		     ELSE Answer END

When using EF Core though rather than writing SQL directly we write Linq queries which get translated to the appropriate SQL query.

To achieve a CASE statement in a GROUP BY you can write the following.

var q = from r in _context.SurveyResultsQ42022s
        group r by new { r.QuestionId, Answer = (r.Answer.StartsWith("Other") ? "Other" : r.Answer) }
        into g
        select new { g.Key.QuestionId, g.Key.Answer, Count = g.Count() };

Combining GROUP BY and CASE in a Linq Query