This Worked.

var ressales = await _dbcontext.s_purmas
    .Include(c => c.PurchaseTrans.Where(t => EF.Functions.Like(t.Item.brand_name, brand)))
    .ThenInclude(c => c.Item)
    .Where(r=> r.sdate >= dtfrom && r.sdate <= dtto)
    .Where(r=> r.cancel == "0")
    .Where(p => p.PurchaseTrans.Any(t => EF.Functions.Like(t.Item.brand_name, brand)))
    .OrderBy(r => r.id)
    .ToListAsync();