squoosh.app is a free, online (and offline) image compression web app and laboratory that lets you tweak many aspects and make comparsions before you render out.
By accessing public data sets (including your own GitHub or Spotify data) through Qlik Associative Engine and APIs, you can experiment and create beautiful visualizations and data-driven apps using powerful search, data retrieval without writing queries, out-of-the-box charts with a single line of code and more. Free. Qlik Playground
Figma is more a web UI design tool than an SVG editor, but it has an excellent toolset and produces well-optimized SVG code. Free.