Audio plugins

For voice

Noise removing

Free: Bertom Denoiser

35$: https://www.waves.com/plugins/ns1-noise-suppressor
The Era seems better (see below).

Bundles or multipurpose

Era: https://accusonus.com/products/audio-repair/era-bundle#pricing (8\$/m!)
Isotope RX8 (\$\$\$\$)

Synths

Free: https://bedroomproducersblog.com/2020/10/30/free-retro-synth/

Other tools

Audio Hijack pour insérer des effets et enregistrer.