No. The repository has GPG signatures for each package. The signature is a hash which is generated using the private developer key. This verifies that the package was compiled by the Debian team. Most other distros also have package signatures, I think.

Reproducible builds means that if you compile the package on your computer from the source code provided by Debian repository, the binary package that you compile will be 100% identical to the binary package in the repository.

Currently, 97.3% of packages in the Debian repository are reproducible. The developers are promising to correct the last ~3% before the next Debian version is released, probably by the end of 2027.

There's a ton of different reasons why compiling a binary on your computer might result in a different file than the binary in the repository. You may have compiled with different libraries. The binary may include timestamps from the compile time. Files inside of a tar may be sorted in a different order.

The purpose of reproducible builds is that you can read the source code, compile the source code, and it will 100% match the binaries in the repository.

Imagine a scenario without reproducible builds. You download a binary from the developers, you download source code from the developers, you compile the code and your binary file is different. How would you know that something nasty isn't hidden inside of the binary from the developer? Distros like Gentoo solve the problem by having each user compile every package on their own machine. Debian's solution is making the packages compile exactly the same on every machine (of the same cpu architecture).