We got a similar result when attempting to access the WP API when 9.8.5 is installed and activated. It did not happen with 8.9.3. The conflict is with the BuddyBoss App plugin (version 1.4.0). And it does not matter if the Disable API switch is on.
The exception is PHP Fatal error: Uncaught Error: Cannot use object of type Closure as array in /home/[site]/wp-content/plugins/buddyboss-app/include/Integrations/SimpleGooglereCaptcha/Main.php:70
It can be driven by a simple http GET to [site]/wp-json from a browser. A result code of 500 is returned.
We can set up a demo site if you like. We can also send stack traces showing some differences in execution path between your plug-in activated and not activated.
I also reported this to BuddyBoss.
Cheers
