As @philko I got something similar on Big Sur, but with another error: 2021-02-02 11:54:56.666469+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Attempting to mount 'smb://baspr@store/TimeMachine' 2021-02-02 11:55:01.038059+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Mounted 'smb://baspr@store/TimeMachine' at '/Volumes/.timemachine/store/10BA71B7-F138-4A36-8A39-6947FA5DF053/TimeMachine' 2021-02-02 11:55:01.038153+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Initial network volume parameters for 'TimeMachine' {disablePrimaryReconnect: 0, disableSecondaryReconnect: 0, reconnectTimeOut: 60, QoS: 0x0, attributes: 0x1C} 2021-02-02 11:55:01.246189+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Configured network volume parameters for 'TimeMachine' {disablePrimaryReconnect: 0, disableSecondaryReconnect: 0, reconnectTimeOut: 30, QoS: 0x20, attributes: 0x1C} 2021-02-02 11:55:01.668781+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/.timemachine/store/10BA71B7-F138-4A36-8A39-6947FA5DF053/TimeMachine' is still valid 2021-02-02 11:55:01.672073+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Mountpoint '/Volumes/.timemachine/store/10BA71B7-F138-4A36-8A39-6947FA5DF053/TimeMachine' is still valid 2021-02-02 11:55:01.680093+0300 0x1162743  Info        0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Creating an encrypted sparsebundle using Case-sensitive APFS filesystem 2021-02-02 11:55:08.885736+0300 0x1162743  Error       0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Failed to create '/Volumes/.timemachine/store/10BA71B7-F138-4A36-8A39-6947FA5DF053/TimeMachine/1C3A8B14-9B42-51E5-9069-FD3C6B7DE771.sparsebundle', results: { }, error: -25300 No such process 2021-02-02 11:55:10.501443+0300 0x1162743  Error       0x1235205            473    0    backupd: (TimeMachine) [com.apple.TimeMachine:General] Backup failed (20: BACKUP_FAILED_DISK_IMAGE_NOT_CREATED)