According to Phil Harvey (exiftool's creator), Quicktime timestamps are supposed to be set to UTC time as per the standard. But it seems a lot of cameras don't do this, so exiftool doesn't assume a timezone and accepts the time as written. See fourth paragraph under Quicktime tags

Exiftool includes an option to correct for this. If you are running exiftool ver 9.40 or later, you can add -api QuickTimeUTC to the command and it will assume that the timestamps are correctly written as UTC and convert them to local time.

I suggest you create a new "CreateDateLocal" tag in which you store the creation time as local time.

You do that by the config.xml. In 'Image::ExifTool::XMP::xmp', you add:

CreateDateLocal => { Groups => { 2 => 'Time' }, Shift => 'Time' },  # Stores the create date in local time (for videos)

It will probably look like this after the insert:

    # XMP tags may be added to existing namespaces:
    'Image::ExifTool::XMP::xmp' => {
        # Example 5.  XMP-xmp:NewXMPxmpTag
        NewXMPxmpTag => { Groups => { 2 => 'Author' } },

        # add more user-defined XMP-xmp tags here...
        CreateDateLocal => { Groups => { 2 => 'Time' } },  # Stores the create date in local time (for videos)
    },

For videos with UTC, run this:
exiftool -r -ext mp4 -api QuickTimeUTC "-CreateDateLocal<CreateDate" .

For videos in local time, run this:
exiftool -r -ext mp4 "-CreateDateLocal<CreateDate" .

You can also run it on images and then simply use "CreateDateLocal" instead of "CreateDate" for organizing. End of simple solution

A bit more advanced solution:

You can create a new composite tag, which falls back to CreateDate, when CreateDateLocal is missing. With this in place, you will only need to tag the videos with UTC timestamp (that is: it will save you from tagging all the images and it will also save you from tagging the videoes that with local timestamp).

Here is how:

Search for "'Image::ExifTool::Composite'" in the config. Inside {}, insert the following:

# TheDateTaken is best attempt to get the date the photo was taken - preferrably in local time
# First the custom tag "CreateDateLocal" is checked. This is expected to be set manually on all videos.
# - For videos with UTC, run this: `exiftool -ext mp4 -api QuickTimeUTC "-CreateDateLocal<CreateDate" .`
# - For videos in local time, run this: `exiftool -ext mp4 "-CreateDateLocal<CreateDate" .`
# If CreateDateLocal isn't set, we asume it is an image. Images are always set in local time.
# There are multiple tags used for storing creation time. We check them all (listed in Desire)

CreateDateLocalWithFallback => {
    Desire => {
        0 => 'CreateDateLocal',
        1 => 'DateTimeOriginal',
        2 => 'CreationDate',
        3 => 'CreateDate',
    },

    Groups => { 2 => 'Time' },
    ValueConv => sub {
        $val = shift;
        # Loop through dates
        foreach $date (@$val) {
            next if not defined $date;
            return $date if ($date =~ /^[12]\d\d\d/);    # if it doesn't start with four digits, skip, as it is not a valid date            
        }               
        return undef;               
    },            
    Shift => 'Time',
    Validate => 'ValidateExifDate($val)',
    PrintConv => '$self->ConvertDateTime($val)',
},

Extend solution by also parsing date from filename

Samsung stores the creation date in the filename. It can be used as fallback. This composite tag can extract the date (to use it in CreateDateLocalWithFallback, simply add "DateFromFilename" to the "Desire" array)

DateFromFilename => {
    Desire => {
        0 => 'OriginalFileName',
        1 => 'FileName',
    },

    Groups => { 2 => 'Time' },
    ValueConv => sub {
        $val = shift;

        foreach $filename (@$val) {
            # See if filename resembles date (it does on Samsung)
            # Samsung naming: "20150827_165859.jpg"
            if ($filename =~ /^\d{8}_\d{6}/) {
                $year = substr($filename, 0, 4);
                $month = substr($filename, 4, 2);
                $day = substr($filename, 6, 2);
                $hour = substr($filename, 9, 2);
                $minute = substr($filename, 11, 2);
                $second = substr($filename, 13, 2);
                $y = int($year);
                $mo = int($month);
                $d = int($day);
                $h = int($hour);
                $mi = int($minute);
                $s = int($second);
            
                #return '2015:08:27 16:58:59';
                #return @$val[0];
                if (
                    (($y > 1900) && ($y < 2400)) &&
                    (($mo >= 1) && ($mo <= 12)) &&
                    (($d >= 1) && ($d <= 31)) &&
                    (($h >= 0) && ($h <= 24)) &&
                    (($mi >= 0) && ($mi <= 60)) &&
                    (($s >= 0) && ($s <= 60))
                ) {
                    # '2015:08:27 16:58:59';
                    return $year . ':' . $month . ':' . $day . ' ' . $hour . ':' . $minute . ':' . $second; 
                }
            }               
        }
        return undef;               
    },            
    Shift => 'Time',
    Validate => 'ValidateExifDate($val)',
    PrintConv => '$self->ConvertDateTime($val)',
    #PrintConvInv => '$self->InverseDateTime($val,0)',
},