Trouble importing Spring Boot Gradle project into Eclipse

I have a Sprint Boot project that I built on another system that I'm trying to import into a new one into Eclipse (4.20.0), and I'm having some issue. It's a Gradle Spring Boot. My build.gradle file is below. I have JKD 16.0.1 install on the machine -- Windows 10.

I've tried importing it with both the Gradle buildship and STS plugins. When I try the Buildship, it fails on the import preview with a big stack dump, with the top line:

org.gradle.tooling.BuildException: Could not fetch model of type 'GradleBuild' using connection to Gradle distribution 'https://services.gradle.org/distributions/gradle-6.8.3-bin.zip'.

When I try Gradle STS, when I hit the "Build Model" button, I tells me errors appeared and to check the log file. The interesting thing I find in there are these:

!ENTRY org.springsource.ide.eclipse.gradle.core 4 0 2021-06-18 17:38:25.575
!MESSAGE Could not determine java version from '16.0.1'.
!STACK 0
java.lang.IllegalArgumentException: Could not determine java version from '16.0.1'.

!MESSAGE Initialize project OrderCreate, Update preview failed due to an error in the referenced Gradle build.
!STACK 0
org.gradle.tooling.BuildException: Could not fetch model of type 'GradleBuild' using connection to Gradle distribution 'https://services.gradle.org/distributions/gradle-6.8.3-bin.zip'.

Caused by: org.gradle.internal.exceptions.LocationAwareException: Initialization script 'C:\Workspaces\Java\K2\.metadata\.plugins\org.eclipse.buildship.core\init.d\eclipsePlugin.gradle'
Could not compile initialization script 'C:\Workspaces\Java\K2\.metadata\.plugins\org.eclipse.buildship.core\init.d\eclipsePlugin.gradle'.

Caused by: org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
General error during semantic analysis: Unsupported class file major version 60

java.lang.IllegalArgumentException: Unsupported class file major version 60

!ENTRY org.springsource.ide.eclipse.gradle.core 4 0 2021-06-18 17:45:56.693
!MESSAGE Could not determine java version from '16.0.1'.
!STACK 0
java.lang.IllegalArgumentException: Could not determine java version from '16.0.1'.
!MESSAGE Not properly disposed SWT resource
!STACK 0
java.lang.Error: SWT Resource was not properly disposed

!MESSAGE Not properly disposed SWT resource
!STACK 0
java.lang.Error: SWT Resource was not properly disposed

I also tried building it from the terminal to get some clues. That gives me the "Unsupported class file major version 60" error.

Could not compile settings file 'C:\Workspaces\Java\K2\OrderCreate\settings.gradle'.
> startup failed:
  General error during semantic analysis: Unsupported class file major version 60

This looks like a real mess. Where do I start solving this?

plugins {
    id 'org.springframework.boot' version '2.4.5'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
    id 'eclipse'
    id "com.diffplug.eclipse.apt" version "3.29.1"
}

group = 'com.bw'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '11'

repositories {
    mavenCentral()
}

ext {
    mapstructVersion = "1.4.2.Final"
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-artemis'
    implementation 'org.springframework.boot:spring-boot-starter-data-mongodb-reactive'
    implementation 'org.springframework.boot:spring-boot-starter-webflux'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    testImplementation 'io.projectreactor:reactor-test'
    
    implementation("org.mapstruct:mapstruct:${mapstructVersion}")
    compileOnly "org.mapstruct:mapstruct-processor:${mapstructVersion}"
    annotationProcessor "org.mapstruct:mapstruct-processor:${mapstructVersion}"
    testAnnotationProcessor "org.mapstruct:mapstruct-processor:${mapstructVersion}"
    
    implementation('org.springframework.boot:spring-boot-starter-data-mongodb')
    testImplementation('de.flapdoodle.embed:de.flapdoodle.embed.mongo')
    implementation 'org.springframework.boot:spring-boot-starter-websocket'
    
    compile group: 'com.google.code.gson', name: 'gson', version: '2.8.5'
}

test {
    useJUnitPlatform()
}

Error from Gradle Buildship:

org.gradle.tooling.BuildException: Could not fetch model of type 'GradleBuild' using connection to Gradle distribution 'https://services.gradle.org/distributions/gradle-6.8.3-bin.zip'.
    at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)

at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:122)
Caused by: org.gradle.internal.exceptions.LocationAwareException: Initialization script 'C:\Workspaces\Java\K2\.metadata\.plugins\org.eclipse.buildship.core\init.d\eclipsePlugin.gradle'
Could not compile initialization script 'C:\Workspaces\Java\K2\.metadata\.plugins\org.eclipse.buildship.core\init.d\eclipsePlugin.gradle'.
    
at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
Caused by: org.gradle.groovy.scripts.ScriptCompilationException: Could not compile initialization script 'C:\Workspaces\Java\K2\.metadata\.plugins\org.eclipse.buildship.core\init.d\eclipsePlugin.gradle'.
    at 

Caused by: org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
General error during semantic analysis: Unsupported class file major version 60

java.lang.IllegalArgumentException: Unsupported class file major version 60
    at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:196)
    at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:177)
    at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:163)
    at groovyjarjarasm.asm.ClassReader.<init>(ClassReader.java:284)
    at org.codehaus.groovy.ast.decompiled.AsmDecompiler.parseClass(AsmDecompiler.java:81)
    at org.codehaus.groovy.control.ClassNodeResolver.findDecompiled(ClassNodeResolver.java:251)
    at org.codehaus.groovy.control.ClassNodeResolver.tryAsLoaderClassOrScript(ClassNodeResolver.java:189)