Other users (mostly from Italy) using iOS 18 are reporting the same issue.
If it keeps crashing, you may need to use the web browser until the problem is fixed. eBay generally releases app updates on Mondays, so check the App Store in a day or two and see if the next update resolves the problem.
I suggest filing a tech report from the website - click the ? icon on the lower right corner of the website from your browser. You can also shake your phone while the app is open to file a tech report, but I think that will only work if you're logged in.
