Also on 32-bit systems, filemtime() also does not work for files with modification time set beyond Jan 2038. It is the dreaded time_t overflow bug for unix seconds.
On windows you can set the system time to any arbitrary future date, and any new files you created or edited will automatically change to that future date.
If exec isn't permitted for some reason, and if you could access the file via an web url (e.g. http://localhost/yourfile.txt), another workaround is to get the Last-Modified time from the HTTP headers (e.g. get_headers(url) ), and parse it as a DateTime object.
I have tested it and it works for years like 2050 and 3012.