In the restricted case that the files are being generated dynamically, then
dinfo = dir('*.rpt*');
[~,newest_idx] = max(datetime({dinfo.date}))
newest_filename = dinfo(newest_idx).name;
What this is doing is looking at the modification date information recorded for each of the files, and picking out the newest one.
In the case where the files might have been sitting around for a while, or might have been transferred between directories, then the modification date becomes less reliable, and you have to start processing the date information
dinfo = dir('*.rpt*');
rawnames = {dinfo.name};
datenames = regexprep(rawnames, '^.*_(\d{8})_(\d{4})\..*$', '$1 $2');
%any name that is not exactly 13 characters is a name that did not follow
%the pattern and we cannot parse.
mask = cellfun(@length, datenames) == 13;
rawnames = rawnames(mask);
datenames = datenames(mask);
filetimes = datetime(datenames);
[~, maxidx] = max(filetimes);
newest_filename = rawnames{maxidx};
