Use more than one query, but prevent duplicates - at scale!

Setup

I have a Gutenberg block (made with ACF), which lets users define certain conditions (e.g. this tag or this date, and a number) to display posts matching these conditions. E.g.: Show newest 5 posts or Show posts between June 1st and June 20th with the tag 'car'. Users can create as many of these blocks as they want, I then parse the conditions into WP_Query and output the posts.

Problem

It can happen, though, that one or more posts would be displayed more than once on such a setup, especially, if a lot of these blocks are used. It could be, for example, that 5 newest and the aforementioned posts with the tag car have 3 posts that are exactly the same. I would like to prevent showing the same posts on one page.

Solution 1: post__not_in + transient or option

Now this is no problem, if I use post__not_in in every WP_Query after the first, saving the IDs returned by WP_Query into a transient or an option, but not only does this not feel the right way to do it, it just does not scale. With a lot of posts, which can be displayed with varying conditions on just one page, performance is an issue and post__not_in seems to be a no go, if it comes to performance.

Solution 2: post__not_in + cached results

Of course, there is always the option to use post__not_in no matter what, push all ids of all queries into some custom object, save it into a transient and use this one on subsequent calls, but here, too, this feels to me as if I am using a way to solve a problem where there is a better way, which I am not seeing. (Also pitty the soul that calls the page when the transient is expired.)

Question

Can anyone help out? (No code needed, although it often helps; I am just interested in the way to do this/to solve this problem.)