OMEN by HP 45L Gaming Desktop GT22-3090 - Intel Ultra 9 285K - 64GB DDR5 - 2TB SSD - GeForce RTX 5090 32GB GDDR7 - Black

It has 2 expansion slots for NVME drives which means there are three total M.2 slots with the first one being taken up by the 2tb stock stock NVME drive. So, those two M.2 slots are empty. Be aware that there is a third M.2 expansion slot that is for media NOT NVME drives.

Although there may not be a USB-C port in the front of the chasse i don't understand why you wouldn't just get a USB-A to USB-C adapter though? After all you should have posted this in comments not questions.

Well, unfortunately you can't be able to install the capture card because the 5090's cooler is so beefy that it covers up all of the expansion slots. So, if I were you i would sell the 4K60S and buy an external capture card (Elgato 4K X). There are two empty M.2 slots that can have NVME SSDs inserted inside of them. Be aware that there is a third M.2 slot that is for WLAN not NVMEs

So, how the CPU gets cooled is by a separate chamber above the chasse called the cryo chamber and since it is outside of the case instead of absorbing hot air from the gpu it gets cool ambient air from the outside. However, since it uses a 240 mm AIO it might not have enough cooling capacity to handle what you might be doing. Furthermore, since it is an AIO it will eventually die in 3-7 years. So i recommend getting an air cooler like the Thermalright Peerless Assassin 120 SE instead of a new AIO because most AIOs are designed to be installed inside of the chasse not in the cryochamber. Finally, yes the back fan is what handles the GPU exhaust the bottom two intake fans on the front provide cool air to the underside of the GPU and since it uses positive pressure where there are three intake fans and one outtake the air that isn't being pulled out by the exhaust fan is pushed out through any available crack. I know, it may sound alarming that that little fan is that handles the gpu exhaust but it is enough. You won't be losing any fps in whatever game your playing anyways.

Operating system Windows 11 Pro Processor Intel® Core™ Ultra 9 285K (up to 5.7 GHz with Intel® Turbo Boost Technology, 36 MB L3 cache, 24 cores, 24 threads)[6,7] Graphics Integrated: Intel® Graphics Discrete: NVIDIA® GeForce RTX™ 5090 (32 GB GDDR7 dedicated) Memory Kingston FURY 64 GB DDR5-5600 MT/s XMP RGB Heatsink (4 x 16 GB) Maximum memory Supports up to 128 GB max system memory Memory slots 4 DIMM Storage 2 TB PCIe® Gen4 NVMe™ M.2 SSD Network interface Realtek RTL8125BGH-CG 10/100/1000/2500 GbE NIC Wireless technology Intel® Wi-Fi 6E AX211 (2x2) and Bluetooth® 5.3 wireless card (supporting gigabit data rate)[11,12,46] Power supply 1200 W 80 Plus Gold certified ATX power supply External I/O Ports Top : 2 USB Type-A 5Gbps signaling rate (HP Sleep and Charge) 1 headphone/microphone combo 1 microphone 2 USB 2.0 Type-A (HP Sleep and Charge) Rear : 1 USB Type-C® 10Gbps signaling rate 2 USB Type-A 5Gbps signaling rate 4 USB 2.0 Type-A 1 3.5 mm audio jack 1 RJ-45 1 Thunderbolt™ 4 with USB Type-C® 40Gbps signaling rate (DisplayPort™ 2.1)[19,52] Expansion slots 1 PCIe x16 1 PCIe x4 3 M.2 (2 PCIe x4 for SSD, 1 for WLAN) Video connector 1 HDMI 2.1b 3 DisplayPort™ 2.1b Audio Features 5.1 surround sound Omen Audio Control Support DTS:X® Ultra Energy efficiency EPEAT® Gold with Climate+ ENERGY STAR® certified Color Black, glass side panel, dark chrome logo Dimensions (W X D X H) 8.03 x 18.5 x 21.85 in Weight 49.82 lb Warranty 1-year limited hardware warranty, limited technical support for software and initial setup (from date of purchase). Software included 1-month Adobe free trial offer McAfee Online Protection 30-day trial PC Game Pass 3-month trial Otter.ai Copilot in Windows with Copilot key 1 month trial for new Microsoft 365 customers[36][24] System Coolers 360 mm LCD liquid cooler System Fan 3 x 120 mm aRGB front fans Sustainable Impact Specifications Molded paper pulp cushion inside box is 100% sustainably sourced and recyclable 10% post-consumer recycled plastic Water based paint[41] Chipset Intel® Z890 Neural Processing Unit (NPU) Intel® AI Boost (13 NPU TOPS)