Hank here from Shopify.
Are you receiving any error messages when you try to set up Shopify payments or is it a case that it is just not appearing for you in Settings > Payments?
Can you share any screenshots of this, or tell me the events that led up to it becoming unavailable?
Also, you are not currently using another payment gateway that may have replaced the Shopify payments section?
If you are not seeing any error messages, can you try opening your admin using incognito mode, to see if this works? If it does, then can you try clearing your cache, and attempt to connect Shopify payments once more?
Let me know, and I'll gladly assist you further with this!
Are you able to share some screenshots or provide some of the steps referenced above?
That way I can assist you with this further.