The concern is that you can’t work fast enough to be a barista? Is this regarding a disability or something else?

To be honest, coffee spots can get pretty hectic during busy hours (e.g. mornings and on weekends).

You can probably find a less popular spot to barista at so you won’t have to worry about volume and speed of service so much.

Order a coffee at a busy time from the spot you’re looking to apply to and see how it all functions. If the baristas seem chill it’s probably a good spot for you.

Good luck!