I'm watching my tone. If you are not sure what magisk doing during its installation - please check their documentation. Magisk patching several partitions (I didn't tell about size, content also is important), at least 'boot' and 'vbmeta'. During uninstalling, magisk can restore only 'boot' but not 'vbmeta'. However the way how incremental OTA is work requires not touched state ALL the partition which present in this OTA (both mentioned above usually there). That condition can't be satisfied by just uninstalling Magisk.