Looking at the log file it seems to move along addinf files for 1857 lines, then this:
0302.862 (1) Beginning creation of dump of uploads (split every: 400 MB)
0302.869 (1) File exists (/var/www/html/wp-content/updraft/backup_2023-03-18-2211_Send_in_the_Clowns_Online_Store_3a24b7e22bb5-uploads5.zip.tmp), but was not modified within the last 30 seconds, so we assume that any previous run has now terminated (time_mod=1679192096, time_now=1679192179, diff=83)
0302.882 (1) Terminate: backup_2023-03-18-2211_Send_in_the_Clowns_Online_Store_3a24b7e22bb5-uploads5.zip.tmp.7asoga exists with activity within the last 30 seconds (time_mod=1679192179, time_now=1679192179, diff=0, size=1192292KB). This likely means that another UpdraftPlus run is at work; so we will exit.
0302.897 (1) Rescheduling resumption 2: moving to 420 seconds from now (1679192599)
0302.920 (1) To decrease the likelihood of overlaps, increasing resumption interval to: 300 + 120 = 420
0333.708 (0) PHP event: code E_WARNING: ZipArchive::close(): Write error: No space left on device (line 4077, wp-content/plugins/updraftplus/backup.php)
So it’s definitely running out of space, the question is how as there is over 20G when it starts.