As a submitter, the goal isn’t to avoid the “penalty”. The point of the “penalty” is to allow for a way to rank every game against every other game as fair as possible.
I think the mistake here is referring to it as a penalty, because it suggests to people they did something wrong with their submission. In reality, it’s more appropriate to call it an adjustment, as it’s serves as a mechanism to more fairly rank every game against every other game.
As an example, if your game got 10 votes with an average rating of 4.5, and someone else got 100 votes with an average rating of 4.5. Do you think it’s fair they rank above you? I think so, since they’ve managed to collect that many more votes while still maintaining a relatively high score.
If there is a fixed number minimum number of ratings required, then it’s going to create a distortion in rankings to the people who collect exactly that number of ratings. A lower number of ratings creates higher variance in the average score compared to a submission with a higher number of ratings. There is a chance the lower-number-of-ratings project has a non-representative score that could bump them above a game that got substantially more ratings.
you get a few ratings and think it’s enough
If you care about your results in a ranked jam, then I recommend participating in the voting process throughout the duration. Rate other people’s work and leave comments. It’s the best way allow others to discover your submission. If you’ve only collected a “few” ratings, then it’s unlikely your raw average score is representative in a way that can be compared to submissions that received substantially more ratings.
how many ratings are needed at least to not get the penalty
The goal is not to tell you to hit a target number of ratings, as that essentially encourages people to try to game the ranking system. Instead, your goal as a participant is to continue to collect ratings. The more ratings you collect, the more “accurate” your average score is relative the number of ratings collected by all other submissions.