1. Compile PHP yourself (no)
2. Use an untrusted third party repo (probably not)
3. Upgrade OS to latest
4. (apparently) Use FreeBSD instead.
For all I know this could change. The current release schedule of PHP is greatly accelerated from what it was 5-10 years ago, and we're all still adjusting I think.
Edit for context: the small business that I work for takes on all kinds of random web work. It's not uncommon at all for us to be asked to rescue an application or website that's still running on PHP 5. For projects that we have initiated, by the time we migrate them all to PHP 8.2, it will be End of Life.
But PHP 7.4 is not compatible in many ways with PHP 7.3, so lumping them together is not OK. As you can see, PHP 8.0 which was only released two years ago, is no longer receiving active support. Definitely, database LTS is not comparable to programming languages. However such rapid releases of breaking versions is a relatively new phenomenon (thanks NodeJS), and I get the feeling that you've never actually supported a software project for 5+ years.
If you can't trust Ondřej Surý's repo, you're gonna be disappointed when you see who maintains the PHP packages in Debian's official repo.