This post is based on https://forums.oracle.com/ords/apexds/post/sql-developer-23-1-clob-view-truncate-long-strings-with-new-9064 which was closed as answered.
However, IMO the bug is still not fixed in the latest version of SQLDev (23.1.1.345.2114).
Here are the steps to reproduce the issue:
Connect to an Oracle Database 23c, and run the following query in a new worksheet:
select to_clob(q'[
line1................................................eol
line3................................................eol
line4................................................eol
line5................................................eol
line6................................................eol
line7................................................eol
]'
) a_clob;
The result looks like this

when I open the result field the following pop-up window is shown:

Then I resize the a_clob
column like this

please note that three dots are displayed at the end of the line. However, when I open the editor, the content is still truncated.
But when I re-run the query the result looks like this:

Now when I double click on the result and then click on the pensil to open the editor, the result looks good:

As @oviwan mentioned in the other thread, a resize of the CLOB result column in the grid and re-query is necessary to see the full CLOB content.
Actually, the behaviour in SQLDev 23.1.0 is 100% identical on my machines.
It worked before in SQLDev 22.2.1.234.
I hope this makes this bug reproducible.