Looking for a trading platform where the platform buys each stock in portfolio according to a percentage you set

I had been using M1 Finance which lets you give a percentage to each stock in your portfolio (totaling 100%). My issue is that M1 would buy stocks under your set percentage until it reached that percentage. All other stocks in our portfolio would not get bought in the mean time. Their strategy is to keep the portfolio balanced based on your percentages. But I see this as essentially buying more of your weakest stock and avoiding winning stocks.

I would like a similar mechanism, assigning each stock in a portfolio a percentage, but when funds are available then the platform buys each stock according the percentage you set. No matter the current value of any stock in the portfolio, the platform buys the percentage you set. If Stock A is set to 25% then for every dollar you deposit it will be $0.25 of Stock A.