Nowhere does it say that Mueller thought there was sufficient evidence to convict.

The Special Counsel therefore did not draw a conclusion — one way or the other — as to whether the examined conduct constituted obstruction [...] the Special Counsel’s report states that “while this report does not conclude that the President committed a crime, it also does not exonerate him.”

It does not make a determination at all. Unless you can point me to where in the report it makes the determination that there was sufficient evidence to convict but cannot indict...

This doesn't say what you're trying to infer

After making a “thorough factual investigation” into these matters, the Special Counsel considered whether to evaluate the conduct under Department standards regarding prosecution and conviction but ultimately determined not to make a traditional prosecutorial judgment.