Maybe the Adaptec 1200p-32i or Broadcom 9600W-16e, depending on requirements. Not a lot of love for Broadcom here (see the neverending and 9500-16i threads) but several other 9600 parts are PCIe 4.0 x8 HBAs supporting 32 internal NVMes.
HighPoint has several x16 to eight M.2 options like the 1508 if less aggressive scale out per slot is ok. I’ve found very little info on HighPoint but the 1508 costs less per drive than the Apex x21 and, unlike the Apex x16, is shipping.
Rather than stay within a 4 TB limit I’d also consider larger options like Micron’s data center lines.