Can you still select go to next line for enter?

Yes, it's still possible.

Does it affect existing posts or only new posts? 

1 hour ago, David N. said:

Does it affect existing posts or only new posts? 

No. Existing posts would be as they are

Thanks.

2 hours ago, Marc Stridgen said:

No. Existing posts would be as they are

Not sure, existing posts may
start to look like
this if they switch now

 

As mine did pre 2015 or whenever it was first introduced when I selected go to new line. All posts prior to that lost the paragraphs. Example 

Likewise, if I had to switch now to start new paragraph

All my posts past 2015

 

would start to

 

look like

 

this.

Edited May 17, 20241 yr by marklcfc

Im not sure what answer I can give there than I already have above, to be honest