The problem is that Gravit will force you to update, if you do not update, they will disable Gravit.
I will purchase Gravit Designer only the next year because I can not afford now.
While you can not afford, you can get: Figma (clone of Sketch, mix of Akira and Gravit), Inkscape, Karbon (now in development since KDE developers received 300k dollars from Handshake) and Vectr are cross-platform. They all, except Figma and Vectr, are native. There is Boxy SVG for macOS and Windows if you want to use for lifetime, but for Linux, it is monthly subscription.
Figma is always free for individual use. Vectr is also free.
Affinity Designer is also cross-platform. If you want to attempt Affinity Designer for Linux using Wine, you can try the tutorial here.