different scholars have different requirements for a sharia compliant currency. im not a taymi but here are ibn tayymiyyahs requirements:

functions as a medium of exchange (i.e. people accept it in exchange for goods and services)

not exposed to debasement or manipulation (government policies, counterfeiting, trimming)

does not serve as a commodity in and of itself (meaning its value is not realized until it is exchanged for something else)

Most currencies you can think of are probably halal (unless they are riba backed). but the buck doesnt stop with 'halal'

we still have to consider and choose the best currency for our situation. many shitcoins are probably halal, but you can still warn against halal things. its halal to drink coffee right before bed, doesnt mean i cant tell people that its a terrible idea