The limit of 200 backups cannot be increased.
You can increase the retention period for the backups but you will have to do manual housekeeping for backups that are no longer needed.
If you select the by backup age, then switch to single rule for all backup sets in that plan, you can add as much as 99 years.
Alternatively, you can keep backups indefinitely, although this will require manual housekeeping to clean up the older backups.