When you see the message 

 Clozure CL kernel debugger:

it means that CCL has crashed. It's in the low-level interactive debugger, which is used to grovel around in the crashed state to figure out what caused it to crash. It isn't really Lisp anymore when you're in the kernel debugger, and won't be able to interact properly with SLIME.

The solution is going to be figuring what's causing CCL to crash, and the right forum for that discussion is the CCL mailing lists or its Github Issues page here:

https://github.com/Clozure/ccl/issues

Slime-devel probably won't be able to help you much.

On Aug 14, 2020, at 7:34 AM, Jan@ziggo <jmvdoorn@ziggo.nl> wrote:

I installed Clozure CL, Aquamacs 3.5 and Slime (through Melpa), made installation settings, but after M-x slime  get following message:

(progn (load "/Users/jvdsmacbook/Library/Preferences/Aquamacs Emacs/Packages/elpa/slime-20200721.1604/swank-loader.lisp" :verbose t) (funcall (read-from-string "swank-loader:init") :from-emacs t) (funcall (read-from-string "swank:start-server") "/var/folders/96/cxqfcbbx0n38n20x9hss8yxr0000gn/T/slime.27376"))

Clozure Common Lisp Version 1.11.5/v1.11.5  (DarwinX8664)

For more information about CCL, please see http://ccl.clozure.com.

CCL is free software.  It is distributed under the terms of the Apache
Licence, Version 2.0.
? ;Loading #P"/Users/jvdsmacbook/Library/Preferences/Aquamacs Emacs/Packages/elpa/slime-20200721.1604/swank-loader.lisp"...sigreturn returned
? for help
[27385] Clozure CL kernel debugger: 

I do not see SLIME and REPL in the topbar of Aquamacs.

Any idea what may be wrong?