https://www.vectorpea.com/ and https://www.photopea.com/ are the lowest barrier to useable alternatives. You can even save them offline and convert to PWA, with very little friction. vectorpea and photopea should handle your .ai files admirably.

Inkscape, Affinity, other open source alternatives exist, but have a remarkably different UI and don't capitalize on your muscle memory.

The feature overlap is bordering on complete, but there are some Adobe Illustrator only perks, for sure. Most of it you can make up for with any of the frontier image AI models.

There are plugins - if you're well versed in how they work, converting between AI and vectorpea should also be a piece of cake with AI.