I’ve just discovered that there are (finally!) 64GB DDR5 SODIMM sticks in existence. Specifically, Crucial CT2K64G56C46S5 is a 128GB kit of two DDR5-5600 CL46-45-45 SODIMMs, and Crucial CT2K64G64C52CS5 is a 128GB kit of two DDR5-6400 CL52-52-52 CSODIMMs (note 46 / 5600 ≈ 52 / 6400, so in absolute terms the latency is, if not stellar, at least not worse on the faster part).
I remember the 7040 series CPUs being picky about RAM, and with clocked SODIMMs (CSODIMMs) in particular there is no guarantee that things will work on memory controllers not designed for those. There are reports of single 64GB CSODIMM sticks working on the 13th gen Intel FW12, but that of course is a very different beast.
If anybody decides to risk it anyway, please post your experiences here!