The MacBook Pro 2021 models have a built-in HDMI port.
HDMI cables you want for HDMI-only Monitors (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:
"Premium High Speed HDMI cable" or that + "with Ethernet" --OR--
"Ultra High Speed HDMI cable" or that + "48G"
Cables with No Certification tags are good for your standard 720p TV set, and not much more.
Just us one of those for one display and the USB-C Digital AV Multiport Adapter - Apple you have now for the other.
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To connect BOTH displays using ONE cable out of the MacBook Pro, the first device must be a genuine ThunderBolt device [display or docking device] and must be connected to the Mac with a genuine ThunderBolt cable.
NB>> Regardless of what docking device is interposed, the Mac does not support Multiple displays over USB-C or DisplayPort cables.