Report Builder can use Segments, but they apply to the entire request...
I'm still more familiar with the older Report Builder, but when you start to build your request, you can choose a segment here:
Filters are different... the best way I can describe this, is that in order to use a segment, you have to have a segment built and part of your components list, and shared to the account running the Report Builder. The segment must also be built to be compatible with Report Builder (though its not shown as it's own compatibility item, I believe it falls under the Reports and Analytics or Workspace compatibility...
Filters on the other hand can provide some basic filtering without the need to create a whole segment, think of it sort of like using the filtering on your Workspace table:
So Filters are limited to "Most Popular" (i.e. the top X items by metric), or a specific list of items (that you can curate here in the settings, or pull from a range of cells)
This can actually be handy if you want items to always show in the same order everytime the report runs (and not be swayed by the metrics). For example, my global suite has 30 websites... on my monthly report, I curate the server list so that the sites always appear in the correct order, so that there is consistency in the display, and my MOM calculations.
If you don't care about the order, you it will default to Most Popular... you can change this from 10 to a higher number... but you cannot pull "unlimited"... if you need to pull everything Report Builder is not the correct tool for the job.
Using a segment would be used like so:
Segments is it's own section, not part of the dimension filtering..
If you need different segments for different dimensions, then you need to make a new Data Block for each pull...
This does make report builder a little more complex than Workspace. Basically each Data Block is a separate API call, and segments are applied to the whole, not just the column.