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Yes, lots of Intel and AMD based SBCs have SO-DIMM slots, but you'll have to accept the 3.5" format.

Regarding RISC-V SBCs, there was serious consideration to release the Milk-V Oasis with SG2380 and LPCAMM2. But this didn't work out as the SG2380 was held up by geopolitical issues.

Orange pi 5 plus has 32gb versions. Pricey though

Not really. Most in the ARM space, at least, are soldered on or you need to switch out the entire compute module. Intel ones (not mini-PCs, but industrial gear and things like the LattePanda) also tend to have soldered RAM.