Debian may seem like the least suitable distro for the desktop, but it doesn't have to be that way. Debian receives critical security updates, so the only thing you're missing out is on feature updates (and fixes for a few annoying, but not deal-breaking bugs).

Still, there are many ways to use newer packages on Debian Bookworm. Below are some of them, ordered from most preferred to least preferred (IMO).

Additional repos

This involves adding custom repos to your APT sources. Programs like Firefox and Wine support this. Some of these have a separate .sources for Debian, so you can be sure you won't get any missing dependency issues.

Also, programs like Steam only require you to install the .deb package they provide — the sources get added automatically.

.deb packages

Usually, this method does not automatically manage updates. Useful if you want a specific version of the package, most likely when the package provided by Debian is too old but the latest package causes dependency issues.
This method isn't recommended if the program has internet access, since older versions may have security vulnerabilities.

Flatpak

This is one of the most popular ways to get up-to-date packages. You can also sandbox programs with ease using Flatseal. The downside is that they take slightly longer to open compared to native packages. You'll also need to set up a service for automatic updates, or remember to update manually when you update native packages via APT. Here is the setup guide for Flatpak.

AppImage

Another distro-independent packaging format, similar to Flatpak. However, AppImages don't have automatic updates, and multiple AppImages can take up more space compared to multiple Flatpaks since they don't share common dependencies. Like with .deb, they're useful if you want a specific version of a package. You can view a list of popular AppImages here.

Prebuilt binaries

Some programs like Firfox and Lutris provide prebuilt binaries. They're less convenient compared to the above formats, especially if they don't automatically handle updates, but not as inconvenient as building from source.

Building from source

This method can be difficult due to old dependency issues or builds failing due to a variety of reasons. Hence, this Good luck.

Debian Testing or Unstable

These are other flavors of Debian that come with newer packages. However, I've noticed that they're not as stable (especially Plasma and KDE software). I'd recommend sticking with Stable and using one of the methods above instead.

Conclusion

This article covers a few ways to get more recent packages on Debian. There are even more ways of doing so — like using Distrobox containers — so experiment and pick the best one that suits your needs.