How can I install l3backend-pdfmode.def?

When I try to compile a .tex file with no additional usepackage, I get the following error:

LaTeX Error: File `l3backend-pdfmode.def’ not found.

Following this thread I ran tlmgr update --all and tlmgr update --self, but I still got the error. I noticed that there is no l3backend-pdfmode.def in the directory l3backend:

C:texlive2020texmf-disttexlatexl3backend
2020/10/16 18:54 .
2020/10/16 18:54 ..
2020/10/16 16:13 24,777 l3backend-dvipdfmx.def
2020/10/16 16:13 32,860 l3backend-dvips.def
2020/10/16 16:13 17,860 l3backend-dvisvgm.def
2020/10/16 16:13 24,060 l3backend-luatex.def
2020/10/16 16:13 23,704 l3backend-pdftex.def
2020/10/16 16:13 26,739 l3backend-xetex.def

I am guessing that I have to add `l3backend-pdfmode.def’ manually, but how can I do that?