[4.9.5]: GraphiQL Bug

What happened?

When launching the GraphiQL explorer in 4.9.5 the screen is blank and the console shows errors:

react-dom.production.min.js:209
Error: Expected String but found number.
at new t (jsonParse.js:125:28)
at g (jsonParse.js:133:12)
at m (jsonParse.js:120:11)
at p (jsonParse.js:57:5)
at f (jsonParse.js:43:26)
at d (jsonParse.js:90:20)
at p (jsonParse.js:59:17)
at f (jsonParse.js:43:26)
at d (jsonParse.js:90:20)
at p (jsonParse.js:59:17)

TypeError: Cannot read properties of null (reading 'options')
at o.value (CraftGraphiQL.js:137:29)
at ss (react-dom.production.min.js:212:132)
at gl (react-dom.production.min.js:255:229)
at t.unstable_runWithPriority (scheduler.production.min.js:19:467)
at qi (react-dom.production.min.js:122:325)
at vl (react-dom.production.min.js:248:370)
at rl (react-dom.production.min.js:239:376)
at Js (react-dom.production.min.js:230:137)
at Ul (react-dom.production.min.js:281:43)
at react-dom.production.min.js:284:301

Uncaught Error: Expected String but found number.
at new t (jsonParse.js:125:28)
at g (jsonParse.js:133:12)
at m (jsonParse.js:120:11)
at p (jsonParse.js:57:5)
at f (jsonParse.js:43:26)
at d (jsonParse.js:90:20)
at p (jsonParse.js:59:17)
at f (jsonParse.js:43:26)
at d (jsonParse.js:90:20)
at p (jsonParse.js:59:17)

This appears to only be happening locally: recently upgraded ddev, don't know what effect that might have. Until recently had no problems with GraphiQL. Have tried clearing all craft caches and rebooting ddev etc.

Craft CMS version

4.9.5

PHP version

8.2

Operating system and version

macOS 15.5

Database type and version

MariaDB 10.5.28

Image driver and version

Imagick 3.8.0 (ImageMagick 6.9.11-60)

Installed plugins and versions

The report points to jsonParse.js and CraftGraphiQL.js in the GraphiQL launch path; begin by reproducing the blank explorer on Craft 4.9.5 with the listed PHP and MariaDB setup and inspect those console errors. Done means GraphiQL loads without the “Expected String but found number” or null-options errors.