If The Choicer Voicer records nothing but silence, you are not alone. This is the game's most widely reported problem. Up front, an honest caveat: the root cause appears to be a limitation in the Godot engine's microphone capture, which shows up especially often on systems with surround or spatial audio configurations. That means there is no guaranteed one-click fix. The steps below are the ones that actually help, in the order worth trying them.
The game records from the system default input device, not necessarily the mic you use in other apps. Open Windows Sound settings, set your microphone as the default input, make sure its level is up and it is not muted, then restart the game. Also check that Windows microphone privacy settings allow desktop apps to use the mic.
Surround-audio setups are the most common thread in reports of this bug. Try:
Restart the game after each change. Audio device changes are usually only picked up on launch.
The developer has published a 0.5.2-dev test build on itch.io that includes microphone recording fixes. It is mentioned on the game's devlog as a build specifically for people hitting this issue. If the stable version will not record for you, download the test build from your itch.io purchase page and see whether it behaves better. Being a dev build, expect some rough edges elsewhere.
If none of the above works, post your setup details (Windows version, mic model, headset software, whether you use surround) on the game's itch.io community board. The developer actively works on this bug, and concrete reports about which configurations fail are what get it fixed.
Some sites list registry hacks, "audio driver boosters", or paid tools as fixes for this bug. None of that addresses an engine-level capture limitation. Save your money and stick to the steps above.
While you wait on a fix, go browse Choicer Voicer packs and find something new to install.