I’ve noticed that QGIS doesn’t always do a good job simplifying geometries when exporting to an SVG file. While you can manually simplify layers, an easier method is as follows:

1) Open Layer Styling

2) Go to Symbology

3) Switch fill to Geometry Generator

4) Use the Simplify Expression to Simplify on the Fly, such as simplifying by 100 map units, which when projected in UTM would be meters.

simplify($geometry,100)