How to handle an "Unhandled Promise Rejection Warning"?

Since some time I get this error message:

(node:4499) UnhandledPromiseRejectionWarning: undefined
(Use `node --trace-warnings ...` to show where the warning was created)
(node:4499) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:4499) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

I have no idea how to find out, where the problem is. I also cannot run any node --trace-warnings command, since strapi is still running. And stopping strapi to then run a node command does nothing.

What do i have to do to find out, where the error is?

strapi 3…6
node 14