The part of the prophecy has a future fulfillent, not a “now” fulfillment...v. 20 And it will become a sign and a witness to the LORD of hosts in the land of Egypt; for they will cry to the LORD because of oppressors, and He will send them a Savior and a Champion (Lit., Mighty One), and He willdeliver them.”
The highway from Egypt to Assyria will be “in that day,” v. 23—there was not a highway from Egypt to Assyria in the days of the Assyrian Empire, nor is there now...nor have Egyptians and Assyrians worshiped together, with Israel as the third party (v. 23-24)—BUT WHEN THEIR MESSIAH RETURNS TO RULE AND REIGN FROM JERUSALEM these things will be fulfilled—in that day.
The entire chapter is about Egypt, and there is not necessarily a chronological sequence as you go from the first verse and continue to the 25th verse.
Separate Issues:
1&2
3
4
5-8
9-10
11-13
14-15
(in that day)
16-17
18-
19-22
23
24-25