Encoding Or Encryption?

Look for anything recognizable or even repeatable because the first impression might be wrong, or perhaps partially correct.  Ask yourself why might that be there?  Is it relevant? Or just a way to throw you off track and create a failure for automated decoding systems?

A lot of malware gets encoded in this way... sometimes more than once too!

A lot of malware will get delivered with Base64 encoding.   Often times, that is Base64 encoded again.  And even then, that code can be obfuscated before execution with some character string that a pre-parser will remove.  Look for any sort of repeating common characters in the message, remove them (XYZ) and decode with Base64.  Then decode again.  You should be able to read the message at this point, or paste it into a LeetSpeak decoder to clean it up back to 'normal' english!

Encoding only hides the message, but encryption protects it.

Notice there are repeating 'obfuscations' of XYZ occuring in the original string.  We could check string length, since Base64 strings need a length divisible by 4.  But then,  that always won't help either.  So try to visualize patterns!  

Remove those repeating sets, and then do a base64 decode.
Malware is often obfuscated and then double base64 encoded, so do another decode of base64.

Now we have a message presenting to us in Leetspeak, so you should be able to decipher the text!  

Or use something like ChatGPT to finalize it into English for you!