With the added information, I'd do something more like
Vtarget=35.4;
[files, path] = uigetfile ('.xlsx', 'MultiSelect', 'on');
if ischar(files), files=cellstr(files); end % handle one file is char string, not cell array
nFiles=numel(files);
hL=gobjects(nFiles,1); % preallocate graphics handles array
for i = 1:nFiles
fullfilename=fullfile(path,files(i)); % use fullfile to build; returns cellstr
tdata=readtable(fullfilename{:}); % and read the spreadsheet to table
ix=interp1(tdata.V,1:height(tdata),Vtarget,'nearest'); % find the nearest point for V
lgd=compose('Vtarget =%f.1',tdata.V(ix)); % build the display string for legend nearest V value
hL(i)=plot(tdata.Time, tdata.P2,'DisplayName',lgd); % plot the P2 variable; don't duplicate same data
if i==1, hold on, end % prepare add more to same figure
end
legend
