EK is releasing the EK-AC Radeon RX 5700 +XT D-RGB water block as a part of the Fluid Gaming lineup. This water block is compatible with reference design AMD Radeon RX 5700 and 5700 XT graphics cards ... EK Releases Radeon RX 5700 (XT) D-RGB aluminum water block
Is annoying that EK up to 3 weeks ago was adamant that they won't release aluminium block for the 5700XT when asked. So had to buy a cooper kit from ground up.
LOL. Galvanic corrosion occurs when you mix metals so what you wrote doesn't apply here. EK Fluid gaming series is all aluminium parts. From blocks to radiators even fittings are made by aluminium and is cheap. With $240 kit you can watercool CPU & GPU, with reservoir, blocks, rads the whole lot because they are made by aluminium not copper.
If I decide to keep my 8600K & Vega 64 going to get a A240R also. Maybe make a dual system with the 3900X & 5700XT AE because the 8600K is on mITX board.