Entity Framework combining multiple queries into one

Think in terms of sets and relational data and not procedurally. It's not easy to determine exactly what you want from your code (which contradicts itself - queryable is set by a call to db.ObjectA.Where(...) which is an IQueryable<ObjectA> but then it is also set by a call to db.ObjectA.First(...), which is an ObjectA; I'll assume you want the IQueryable<ObjectA> since later code references queryable.Any(...)) but here's my guess:

var days = DateHelper.EachDay( startDate, endDate );

var activeDaysIsLogicCorrectFlags = db.Operations
    // get days that are "active"
    .Where( op => op.IsActive && days.Contains( op.Day ) )
    // join with ObjectA's to filter for active ObjectA's
    // is there a nav property you could use instead?
    // use GroupJoin for use with `Any(...)` in results
    .GroupJoin( db.ObjectA, op => op.Day, oa => oa.Day, ( op, oaGroup ) => new
        {
            //Operation = op,
            // projecting Operation.Day since that's what your foreach loop is using
            Day = op.Day,
            IsLogicACorrect = oaGroup.Any( oa => oa.ObjectACount == 5 ),
            // if IsLogicBCorrect can be determined from the collection of ObjectA's:
            //IsLogicBCorrect = oaGroup.Any( oa => oa.ObjectBCount == 3 ),
        } );

The results are an IQueryable of an anonymous type that maps an "active" Operation.Day with your logic for IsLogicACorrect. For your other IsLogicXCorrect flags, if they can all be determined using the ObjecetA group aoGroup, simply add them to the GroupJoin result selector (as shown in the commented-out property). If those flags need their own groupings (e.g. need to use ObjectB group to determine IsLogicBCorrect, then add additional calls to GroupJoin as shown above but using their respective DbSet and properties. For example, if you need to use db.ObjectB for IsLogicBCorrect:

var activeDaysIsLogicCorrectFlags =
    <existing logic from above>
    .GroupJoin( db.ObjectB, at => at.Day, ob => ob.Day, ( at, obGroup ) => new
        {
            // project all previous results
            at.Day,
            at.IsLogicACorrect,
            // new flag
            IsLogicBCorrecet = obGroup.Any( ob => ob.ObjectBCount == 3 ),
        } );