What is the difference between 这个 and 此?
这 is more colloquial, usually followed by a classifier

此 is more literary, it does not need classifier, and more often followed by a single character word



See Examples:
此人= 這個人
此事= 這件事
此地= 這個地方
此物= 這件東西
此時= 這個時候
此刻= 這個時刻
此心= 這顆心
此案= 這宗案
The classifier after 這 can often be omitted. For example: 這個地方--&gt; 這地方; 這件東西--&gt;這東西.
Since classifiers work with counting words,  we can write 這一個地方; 這三件東西.
But we don't usually use counting word with 此
'此一地方' , '此三東西. just sound unnatural.