Are triple-slot GPUs betterworse than double-slot?

Are PCIe and PCIe backward and forward compatible? How does PCIe influence SSD and GPU selection? Is upgrading to PCIe worth it?

AV1 decode Configurable to: M3 Pro with 12-core CPU and 18-core GPU, M3 Max with 14-core CPU and 30-core GPU SDXC card slot HDMI port mm headphone jack

3 hot chillies slot Motherboard, ITX ; Max CPU Cooler Height, 67mm ; SFXSFX-L · GPU 345mm length-Within 65mm thickness ; ATX140mm, GPU 345mm length-Within

300 slot The thickness of these cards also typically occupies the space of 2 PCIe slots PCI slots at mm), taking up 3 PCIe slots, while an Asus