documentclass[11pt]{article}
usepackage[a4paper, portrait, margin=1in]{geometry}
usepackage{adjustbox}
usepackage{tabularx}
usepackage{booktabs,csvsimple}
usepackage{pdflscape}

[...]

begin{landscape}
thispagestyle{empty}
    begin{table}[ht]
        begin{adjustbox}{max width=textwidth}
            csvautobooktabular[]{csvs/large_table.csv}
        end{adjustbox}
        caption{small{Blah blah blah}}
        label{tab:test}
    end{table}
end{landscape}

documentclass[11pt]{article}
usepackage[a4paper, portrait, margin=1in]{geometry}
usepackage{adjustbox}
usepackage{tabularx}
usepackage{booktabs,csvsimple}
usepackage{pdflscape}

[...]

begin{landscape}
thispagestyle{empty}
newgeometry{margin=1cm}
    begin{table}[ht]
        begin{adjustbox}{max width=textwidth}
            csvautobooktabular[]{csvs/large_table.csv}
        end{adjustbox}
        caption{small{Blah blah blah}}
        label{tab:test}
    end{table}
end{landscape}

newgeometry{margin=1cm,textwidth=paperwidth-2cm}