Brahms himself did not use the title Passacaglia, but the last movement of his fourth symphony is certainly seen as a passacaglia, for which Bach was probably the source of inspiration. It is a very effective work, the orchestration of which on organ can be imitated well by the right choice of registration. Transitional dynamics are not necessary, the sound can be changed per variation or group of variations.
For this organ arrangement, the piece has been transposed from E minor to C minor. This puts it in the same key as Bach's Passacaglia, and it has already served as a counterpart in concerts that opened with Bach's Passacaglia and ended with Brahms's. In this position, it also fits into the compass of C-c”’, which means it can be played on almost all organs.
The music (as a digital version) is available at https://www.valeurajoutee.eu/en/product/joh-brahms-bew-reitze-smits-passacaglia-uit-de-vierde-symfonie/.
There is also a recording on that page.