Extracting with regex two conditions of some text

My code doesn't work:

 regexp_substr('Lorem ipsum dolor sit amet. consectetur', '([^(.|()]+)|((.){0,9})')

The text should end with a dot, and if it does not have a dot, then it should have a maximum of 10 characters. Is it even possible to do this?

Two examples text:

1. Lorem ipsum dolor sit amet. consectetur
2. Donec quis turpis sed sapien ullamcorper viverra sodales a est

This is what it should look like

1. Lorem ipsum dolor sit amet
2. Donec quis

You can use a replacing approach here:

REGEXP_REPLACE('Lorem ipsum dolor sit amet. consectetur',
                      '^([^.]+)\..*|^(.{10}).*',
                      '\1\2') 

See this regex demo.

Details:

• ^([^.]+)\..* - if a string has a dot, capture the text before it, and then match the dot with the rest of the string:
  • ^ - start of string
  • ([^.]+) - Group 1 (\1): any one or more chars other than .
  • \. - a dot
  • .* - any zero or more chars as many as possible
• | - or
• ^(.{10}).* - match and capture (into Group 2) the 10 chars ((.{10})) at the beginning of the string (^), then match the rest of the string.

The replacement is two backreferences to the captured values.