Work on PHP 7.3 by any chance?

Hello, I have modified the latest version with support for PHP 8.1

So you have t.s 5.6 working with PHP friends 8.1? I was looking for a progressive experience in learning how to update PHP code for t.s 1.3.9 upto 5.6 like bootstrap responsive design, memcache get rid of a few things just wanted to test a version of this capability on my new demo services that's all I seen ages ago a 7.3 or 7.1 or similar with a 5.6 engine base using t.s 7.0+ skins still a thing right?like if I completely rewrite engine base using u232v5 I am okay to run live site for members without getting any hacker hiesting our mainframe development manager sources right?
1.update to gazelle or u232 v5 standards
2. secure any mysqli vuniablities
3 add memcache
4 add bootstrap 5 or v4
5. Add new sucirity over xam code for example is doable?