I have observed this under Windows 10, maybe other OS are also affected:

Install a clean Eclipse 2020-12 (4.18) IDE from the website, probably through installer, choose "Eclipse IDE for Enterprise Java Developers". Until here there is no problem.

Now, install the JBoss tools according to https://tools.jboss.org/downloads/jbosstools/2020-09/4.18.0.Final.html.

Choose the "JBoss Web and Java EE Development" option.

Now something strange happens in the normal eclipse IDE (/no special windows opened):

When you type Alt+A, you would expect that you use the mnemonic of pulldown menu "Search" (the "a" is underlined to hint that) to respond and open the Search menu.

However, that no longer works. Instead the "Search" menu responds to Alt+S which is double bad because that mnemonic belongs to the "Source" menu. So when you press Alt+S several times, you switch b etween those two menus but neither opens.

uninstalling the JBoss tools reverts the pulldown menu behaviour back to normal.