How much more would you want to show? If after seeing this much of the topic, instead of clicking “Expand”, why not just go to the topic - if it interests someone that much?
If you want to change the maximum number of characters from the default 300 to something higher, you can go to Settings/Posting and scroll down to post excerpt maxlength (Maximum length of a post excerpt / summary) and increase the number. But you should remember… this is a summary, and that’s what it’s meant for. 