Get max date from each specific user ID without repeating IDs using XSLT

I have the following XML

<?xml version='1.0' encoding='UTF-8'?>
<root>
    <Data>
        <Record>
            <User>1</User>
            <LastModified>1/1/2023</LastModified>
            <UniversityDegree>University of Texas Bachelors</UniversityDegree>
        </Record>
        <Record>
            <User>1</User>
            <LastModified>1/11/2023</LastModified>
            <UniversityDegree>University of Missouri Masters</UniversityDegree>
        </Record>
        <Record>
            <User>2</User>
            <LastModified>1/1/2024</LastModified>
            <UniversityDegree>University of Texas Bachelors</UniversityDegree>
        </Record>
        <Record>
            <User>2</User>
            <LastModified>1/12/2023</LastModified>
            <UniversityDegree>University of Missouri Masters</UniversityDegree>
        </Record>
        <Record>
            <User>3</User>
            <LastModified>5/7/2023</LastModified>
            <UniversityDegree>University of Texas Bachelors</UniversityDegree>
        </Record>
        <Record>
            <User>3</User>
            <LastModified>9/8/2023</LastModified>
            <UniversityDegree>University of Missouri Masters</UniversityDegree>
        </Record>
        <Record>
            <User>4</User>
            <LastModified>24/1/2023</LastModified>
            <UniversityDegree>University of Texas Bachelors</UniversityDegree>
        </Record>
        <Record>
            <User>4</User>
            <LastModified>28/9/2023</LastModified>
            <UniversityDegree>University of Missouri Masters</UniversityDegree>
        </Record>
        <Record>
            <User>5</User>
            <LastModified>15/3/2023</LastModified>
            <UniversityDegree>University of Texas Bachelors</UniversityDegree>
        </Record>
        <Record>
            <User>5</User>
            <LastModified>10/3/2023</LastModified>
            <UniversityDegree>University of Missouri Masters</UniversityDegree>
        </Record>
    </Data>
</root>

And I need to extract the max date of each user, so for example out of use 5 the max date from 15/3/2023 and 10/3/2023 is 15/3/2023 and show it like this:

<?xml version="1.0" encoding="UTF-8"?>
<LastModified>15/3/2023</LastModified>
<User>5</User>

I've done the following,

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <xsl:output method="xml" indent="yes"/>
   <xsl:template match="//root">
      <xsl:for-each select="//Record">
         <xsl:sort select="number(substring(LastModified, 7, 4))" order="descending"/>
         <xsl:sort select="number(substring(LastModified, 3, 2))" order="descending"/>
         <xsl:sort select="number(substring(LastModified, 1, 2))" order="descending"/>
         
         
         <xsl:if test="position() = 1">
            <xsl:copy-of select="LastModified"/>
            <xsl:copy-of select="User"/>
            <Source>SF</Source>
         </xsl:if>

      </xsl:for-each>
   </xsl:template>
</xsl:stylesheet>

Which returns,

<?xml version="1.0" encoding="UTF-8"?>
<LastModified>1/1/2024</LastModified>
<User>2</User>
<Source>SF</Source>

But it only returns the first sorted record due to the position 1 if. I would need to get the max date of each of the users without having duplicates. If I remove the IF condition, I get everything sorted but Users are repeated,

<?xml version="1.0" encoding="UTF-8"?>
<LastModified>1/1/2024</LastModified>
<User>2</User>
<Source>SF</Source>
<LastModified>1/12/2023</LastModified>
<User>2</User>
<Source>SF</Source>
<LastModified>1/11/2023</LastModified>
<User>1</User>
<Source>SF</Source>
<LastModified>28/9/2023</LastModified>
<User>4</User>
<Source>SF</Source>
<LastModified>24/1/2023</LastModified>
<User>4</User>
<Source>SF</Source>
<LastModified>15/3/2023</LastModified>
<User>5</User>
<Source>SF</Source>
<LastModified>10/3/2023</LastModified>
<User>5</User>
<Source>SF</Source>
<LastModified>1/1/2023</LastModified>
<User>1</User>
<Source>SF</Source>
<LastModified>5/7/2023</LastModified>
<User>3</User>
<Source>SF</Source>
<LastModified>9/8/2023</LastModified>
<User>3</User>
<Source>SF</Source>

Try perhaps something like:

XSLT 2.0

<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/root">
	<result>
		<xsl:for-each-group select="Data/Record" group-by="User">
			<user>
				<xsl:for-each select="current-group()">
					<xsl:sort select="tokenize(LastModified, '/')[3]" data-type="number" order="descending"/>
					<xsl:sort select="tokenize(LastModified, '/')[2]" data-type="number" order="descending"/>
					<xsl:sort select="tokenize(LastModified, '/')[1]" data-type="number" order="descending"/>
					<xsl:if test="position() = 1">
						<xsl:copy-of select="LastModified, User"/>
						<Source>SF</Source>
					</xsl:if>
				</xsl:for-each>
			</user>
 		</xsl:for-each-group>
	</result>
</xsl:template>

</xsl:stylesheet>

Caveat: not tested very thoroughly.

Here is a somewhat different approach that's not necessarily better, but it takes advantage of more XSLT 2.0 features:

XSLT 2.0

<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:mf="http://www.example.com/mf"
exclude-result-prefixes="xs mf">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/root">
	<result>
		<xsl:for-each-group select="Data/Record" group-by="User">
			<user>
				<LastModified>
					<xsl:value-of select="format-date(max(current-group()/LastModified/mf:reformat-date(.)), '[D]/[M]/[Y]')"/>
				</LastModified>
				<xsl:copy-of select="User"/>
				<Source>SF</Source>
			</user>
 		</xsl:for-each-group>
	</result>
</xsl:template>

<xsl:function name="mf:reformat-date" as="xs:date">
	<!-- expected input format: d/m/y -->
	<xsl:param name="date"/> 
	<xsl:variable name="components" select="for $t in tokenize($date, '/') return xs:integer($t)" />
	<xsl:value-of select="format-number($components[3], '0000'), format-number($components[2], '00'), format-number($components[1], '00')" separator="-"/>
</xsl:function>

</xsl:stylesheet>