@test29 there is no set limit on the course enrollment size. The experience depends on the kinds of content in the course that impacts course size, number of assessments, assessments you are utilizing; are you having students complete assignments within a small window or time, etc.
As these increase, users may experience lags in the content loading, gradebook refresh times, saving time etc. The strategies listed in the above links (and other links from within them) elaborate on there.
Do reach out to your Customer Success Manager so that they can work with you to help optimize student, teacher and admin experience.