I reviewed quite a few posts and looks like this is NOT possible without add-ons but still wanted to check.
Summary is a required field in JIRA cloud platform and I do NOT see a way to make it optional on JIRA software project field configuration. To workaround this problem, I could neither find a way to set a default value in Summary field on the create issue screen nor add a bold text (injecting javascript code into the description box of Summary field). We do not want to go for add-ons just for this purpose, so wanted to run by community for seeking expert solutions.