MantBox 15ax is a very good and capable device, but its performance is being limited because of the restricted channel selection range.
MikroTik should consider expanding the available channel range on the MantBox 15ax, allowing users to manually select the channels according to their local RF environment, similar to what is available on MikroTik AC-series APs.
Having more channel options would help users avoid interference, select cleaner frequencies, and achieve better and more consistent performance.
Please consider expanding the channel selection range in a future RouterOS/firmware update.
If there's a difference between what you want to use vs what you're allowed to use, you'll have to use what you're allowed to use.
If there are errors in the regulatory information used by MikroTik you'll have to report it. But I highly doubt it.