Another alternative: https://gist.github.com/muink/b7f506e4f210633d466c5c8e48440384

urldecode.jq

def urldecode:
		def hex2dec:
			{"0":0,"1":1,"2":2,"3":3,"4":4,"5":5,"6":6,"7":7,"8":8,"9":9,"A":10,"B":11,"C":12,"D":13,"E":14,"F":15} as $hexTable
			| [1,16,256,4096,65536,1048576,16777216,268435456] as $pow16
			| def str2dec:
				split("") | reverse as $arr
				| last( foreach range(length) as $i (0; . + $hexTable[($arr[$i]|ascii_upcase)] * $pow16[$i]) );
			if type == "string" then
				str2dec
			elif type == "array" then
				last(
					label $out | foreach range(length) as $i (.;
						if (.[$i]|type) == "string" then
							.[$i]=(.[$i]|str2dec)
						else null, break $out end
					)
				)
			else empty end;
		def utf82uni:
			def loop($i):
				if $i >= length then empty
				elif .[$i] >= 240 then (.[$i+3]-128) + 64*(.[$i+2]-128) + 4096*(.[$i+1]-128) + 262144*(.[$i]-240), loop($i+4)
				elif .[$i] >= 224 then (.[$i+2]-128) + 64*(.[$i+1]-128) + 4096*(.[$i]-224), loop($i+3)
				elif .[$i] >= 192 then (.[$i+1]-128) + 64*(.[$i]-192), loop($i+2)
				else .[$i], loop($i+1)
				end;
			[loop(0)];
		gsub("(?<x>(?:%[[:xdigit:]]{2})+)"; .x | .[1:] | split("%") | hex2dec | utf82uni | implode);
	urldecode