I may have found the answer! I just ordered it!

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https://www.amazon.com/gp/product/B07LC7HVHW/ref=ox_sc_act_title_3?smid=A2VZTJP6N0Z6QL&psc=1

SOLVED:

Just following up in case anyone ever needs this info. I tried five different IR extenders that plug directly into the cable box, and none worked.

I finally broke down and tried this one (has its own power, and sticks to the outside of the cable box. Works perfectly:

BAFX Products - All-in-One... https://www.amazon.com/dp/B07LC7HVHW?ref=ppx_pop_mob_ap_share

This is fucking hilarious

edit: but for real, I think something like this is what you're looking for, or for better range and the ability to hide everything, this one works really well, but you will need to recharge the little battery occasionally.