Weighted Block Randomization

I don't know of a clear built-in way to do this. But perhaps this is something you can achieve by combining block randomization with branch logic on quotas. Where the quotas help count how many times the blocks have been shown and are set to get you to the 0.25/0.75 split. It should work if you have a targeted number of completed surveys this will work for you.
This particular link to the Qualtrics Support page should help you figure out how to stop showing a block once the quota is met, helping you force the 0.25/0.75 split. https://www.qualtrics.com/support/survey-platform/survey-module/survey-tools/quotas/#SpecifyingQuotaActions

Another option could be to repeat block to match the split required. So, for a 25-75 split, you could have 3 blocks of one kind and 1 of the other, all randomized equally.