How to sort by particular joural entry by num, e.g. num 5 to 8.

Do you mean sort a report?  If so many transaction detail reports have a sort option at the top of the report.

Here's another "fun" QBO quirk:

Follow the respondent's directions to sort journal entries by "Num," ascending.  Here's my result (in part):

Num

1

10

100

101

102

103

...

2

20

200

201

202

...

Hmmm...I guess QBO doesn't know that "Num" is actually an integer (which don't get sorted by their first digit) and not just a character string (which do)!  Pitiful...