Measurement of the diffuse astrophysical neutrino flux over six seasons using cascade events from the Baikal-GVD expanding telescope

N.M. Budnev V.A. Chadymov A.S. Chepurnov V.Y. Dik A.N. Dmitrieva G.V. Domogatsky A.A. Doroshenko R. Dvornick\'y A.N. Dyachok Zh.-A.M. Dzhilkibaev E. Eckerov\'a T.V. Elzhov V.N. Fomin A.R. Gafarov K.V. Golubkov T.I. Gress K.G. Kebkal V.K. Kebkal I.V. Kharuk S.S. Khokhlov E.V. Khramov M.M. Kolbin S.O. Koligaev K.V. Konischev A.V. Korobchenko A.P. Koshechkin V.A. Kozhin M.V. Kruglov V.F. Kulepov A.A. Kulikov Y.E. Lemeshev M.V. Lisitsin S.V. Lovtsov R.R. Mirgazov D.V. Naumov A.S. Nikolaev I.A. Perevalova A.A. Petrukhin D.P. Petukhov E.N. Pliskovsky M.I. Rozanov E.V. Ryabov G.B. Safronov B.A. Shaybonov V.Y. Shishkin E.V. Shirokov F. \v{S}imkovic A.E. Sirenko A.V. Skurikhin A.G. Solovjev M.N. Sorokovikov I. \v{S}tekl A.P. Stromakov O.V. Suvorova V.A. Tabolenko V.I. Tretjak B.B. Ulzutuev Y.V. Yablokova D.N. Zaborov S.I. Zavjalov D.Y. Zvezdov