Memory Error (500) For SMTP Settings After Upgrading to 5.35.1
What I think happened is that added the encryption key after I did the upgrade. I am not sure how I did this.  This was then causing the SMTP key not to be able to be read.
I got the idea that maybe I could force blank values into the STMP form. While there I found this code.
if (!empty($this-&gt;_defaults['smtpPassword'])) {
          $this-&gt;_defaults['smtpPassword'] = \Civi::service('crypto.token')-&gt;decrypt($this-&gt;_defaults['smtpPassword']$
        }

I commented this out and the form loaded.  I saved without the key in the civicrm.settings.php file and then with the key again.
Now everything works correctly again.