Clients website went down because he had an extremely dated website and his hosting provider updated their PHP

Hi everyone.

I currently have a client who has hired me to develop a new website for him because his previous site was made in the early 90’s and was extremely outdated.

Problem is, as I was building his site on a seperate test domain, his website went down. I contacted his hosting provider and found that they had recently updated their PHP and that this was likely the cause of his website crashing and being delisted from search results.

I have since transferred his domain to my Godaddy account and launched a new website on the domain but the site is not showing up despite the site using the same keywords and similar content.

Is this just a matter of the site being new and Google not yet crawling the site? His old website was ranking despite a lack of SSL and poor UX because it had been around for a long time and was one of the first in his niche…

Mostly posting because I’d like to hear thoughts from some more experienced SEO people about what I can do or how best to make sense of this to the client.

Sorry if this is annoying in any way. Just trying my best to find a solution. Thanks.