Mylyn wants to drop from simrel, at least they express that following releases from mylyn core is time consuming and they have serious issues with release train[1]. 

When installing everything from Jboss update site into BYOE, I have multiple errors in console and mylyn cannot starts: 

 
eclipse.buildId=4.21.0.I20210818-1800
java.version=11.0.12
java.vendor=Red Hat, Inc.
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=fr_FR
Command-line arguments: -os linux -ws gtk -arch x86_64

org.eclipse.mylyn.tasks.ui
Error
Mon Sep 06 09:57:45 CEST 2021
FrameworkEvent ERROR

org.osgi.framework.BundleException: Could not resolve module: org.eclipse.mylyn.tasks.ui [992]
Unresolved requirement: Require-Bundle: org.eclipse.mylyn.commons.notifications.feed; bundle-version="1.0.0"
-> Bundle-SymbolicName: org.eclipse.mylyn.commons.notifications.feed; bundle-version="1.18.0.v20190930-2131"; singleton:="true"
org.eclipse.mylyn.commons.notifications.feed [980]
No resolution report for the bundle. Bundle was not resolved because of a uses constraint violation.
org.apache.felix.resolver.reason.ReasonException: Uses constraint violation. Unable to resolve resource org.eclipse.mylyn.commons.notifications.feed [osgi.identity; type="osgi.bundle"; version:Version="1.18.0.v20190930-2131"; osgi.identity="org.eclipse.mylyn.commons.notifications.feed"; singleton:="true"] because it is exposed to package 'javax.xml.bind' from resources javax.xml.bind [osgi.identity; type="osgi.bundle"; version:Version="2.2.0.v201105210648"; osgi.identity="javax.xml.bind"] and jakarta.xml.bind [osgi.identity; type="osgi.bundle"; version:Version="2.3.3.v20201118-1818"; osgi.identity="jakarta.xml.bind"] via two dependency chains.

Chain 1:
org.eclipse.mylyn.commons.notifications.feed [osgi.identity; type="osgi.bundle"; version:Version="1.18.0.v20190930-2131"; osgi.identity="org.eclipse.mylyn.commons.notifications.feed"; singleton:="true"]
require: (&(osgi.wiring.bundle=javax.xml.bind)(bundle-version>=2.2.0))
 
provide: osgi.wiring.bundle: javax.xml.bind
javax.xml.bind [osgi.identity; type="osgi.bundle"; version:Version="2.2.0.v201105210648"; osgi.identity="javax.xml.bind"]

Chain 2:
org.eclipse.mylyn.commons.notifications.feed [osgi.identity; type="osgi.bundle"; version:Version="1.18.0.v20190930-2131"; osgi.identity="org.eclipse.mylyn.commons.notifications.feed"; singleton:="true"]
require: (&(osgi.wiring.bundle=com.sun.xml.bind)(bundle-version>=2.2.0))
 
provide: osgi.wiring.bundle; bundle-version:Version="2.3.3.v20201118-1818"; osgi.wiring.bundle="com.sun.xml.bind"
com.sun.xml.bind [osgi.identity; type="osgi.bundle"; version:Version="2.3.3.v20201118-1818"; osgi.identity="com.sun.xml.bind"]
import: (&(osgi.wiring.package=javax.xml.bind)(&(version>=2.3.3)(!(version>=2.3.4))))
 
export: osgi.wiring.package: javax.xml.bind
jakarta.xml.bind [osgi.identity; type="osgi.bundle"; version:Version="2.3.3.v20201118-1818"; osgi.identity="jakarta.xml.bind"]
at org.eclipse.osgi.container.Module.start(Module.java:463)
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.lambda$1(ModuleContainer.java:1834)
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.incStartLevel(ModuleContainer.java:1829)
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.incStartLevel(ModuleContainer.java:1775)
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.doContainerStartLevel(ModuleContainer.java:1739)
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.dispatchEvent(ModuleContainer.java:1661)
at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.dispatchEvent(ModuleContainer.java:1)
at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:228)
at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(EventManager.java:339)

[1]https://www.eclipse.org/lists/cross-project-issues-dev/msg18358.html