The same way you do it in rust, use wrappers for all memory allocation.
C++ has had RAII forever, since C++11(2024 btw now) have actually good wrappers, Box = std::unique_ptr, whatever the ref counter version is = std::shared_pte.
Do the other things he already said to do, ie clang-tidy with the correct rule will warn/error on any raw pointer usage. You don't need to "not make mistakes". If you never use raw pointers, other than these specific places you tell the linter that it was fine and you have checked then by default it will be memory safe. Does that sound familiar?
"But we don't need a linter in Rust!" It's just built into the LLVM frontend called the rust compiler. If it bugs you so much build a custom executable that runs the linter then the c++ compiler and call it your own internal compiler. First line of code can be "#!/bin/sh"...
If you say you aren't talking about Rust but one of the GC languages, then I agree with you, write it in that other language but then the correct solution is to rewrite the software in the first place since it was never written in the correct language to start with. Rewriting something in Rust is likely the same amount of complexity as fixing the C++ code, if you however first need to learn Rust well there's a reason I am not exactly pro rust ans yes I bave tried to use it in a proper complex project, all deadlines were missed and we ended up writing it in modern safe C++ instead purely because the language didn't force us to make up some obscure abstraction to appease the borrow checker.