Because this was specifically addressed, I did not bother replying. My feeling is that, if you want to address someone personally, use the private message system.
Having said that, I would convert the site to Bootstrap 5 as a matter of priority. You will be building on the future with the riddance of jQuery.
See this excellent article by @Teodor
If you want to use another method, have a look at
All of this should be done in a new project by duplicating the current project.
Once you have made the Bootstrap change, you have a choice of PHP or Node.
I have to agree with Brian (@Hyperbytes), that Node is definitely the way to go, again with the eye on the future. I won't go into details here, but please believe this octogenarian.
To make the change to PHP 8.3, again start a new project by duplicating an existing project. Then be wary of what this article states:
PHP: Migrating from PHP 7.4.x to PHP 8.0.x - Manual.
If the wiser choice has been made, it will require starting a whole new project based on NodeJS. There will be a significant change in the structure of the project files, partially because of the Express templating engine. However, all that you have done to create a Bootstrap 5 site, will not be lost. A lot of copying and pasting will fix the client side. The server side will consist of the creation of new API's.
With Node, you will go through a difficult period. But the end result will be very rewarding for the future. It's called evolution.