Eclipse Buildpath issue for after Maven : Update Project - maven

Question

We are working on Sprint Boot in eclipse IDE Oxygen 4.7.3a with RTC Client v6.0.5
RTC - code repository where we keep our code base
The problem is whenever we do
Right click Project > Maven > Update Project (Force Update of Snapshots/Releases)
JRE System Library is downgraded to J2SE-1.5 from Workspace default JRE (java-11-openjdk)
It makes us to fix Java build path again to openjdk-11 manually. How can we avoid auto JRE downgrade after Maven > Update Project
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.5.6</version>
<relativePath /> <!-- lookup parent from repository -->
</parent>
<groupId>com.xx.rt.edgeservice.discoveryserver</groupId>
<artifactId>rt-edge-service-discovery</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>rt-edge-service-discovery</name>
<description>XX Service Discovery</description>
<properties>
<java.version>11</java.version>
<spring-cloud.version>2020.0.4</spring-cloud.version>
<jacoco.version>0.8.6</jacoco.version>
<sonar.java.coveragePlugin>jacoco</sonar.java.coveragePlugin>
<sonar.dynamicAnalysis>reuseReports</sonar.dynamicAnalysis>
<sonar.jacoco.reportPath>${project.basedir}/../target/jacoco.exec</sonar.jacoco.reportPath>
<sonar.language>java</sonar.language>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>org.sonarsource.scanner.maven</groupId>
<artifactId>sonar-maven-plugin</artifactId>
<version>3.4.0.905</version>
</plugin>
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>${jacoco.version}</version>
<executions>
<execution>
<id>jacoco-initialize</id>
<goals>
<goal>prepare-agent</goal>
</goals>
</execution>
<execution>
<id>jacoco-site</id>
<phase>package</phase>
<goals>
<goal>report</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
</repository>
</repositories>
</project>

Answer 1

For Simple Maven Project
M2Eclipse is using target parameter from maven-compiler-plugin information to set your eclipse project.
The default value is 1.5, if you are using a maven version under 3.8.0.
So you need to configure at maven level which java version you want to target by changing your pom.xml with :
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.10.1</version>
<configuration>
<source>11</source>
<target>11</target>
</configuration>
</plugin>
</plugins>
</build>
OR
<properties>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
About java version number, I think those both syntax (1.x and x) are supported. (E.g. for java8, 1.8 or 8)
For Sping Boot
It should work to use :
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>version (e.g 2.5.6)</version>
</parent>
<properties>
<java.version>11</java.version>
</properties>
If you look at spring-boot-starter-parent, you will see that java.version properties is used to set maven.compiler.source and maven.compiler.target