Can you verify this? Incremental backups are not working:

# COMPLETELY NEW INSTANCE:
systemctl stop mariadb; rm -fr /var/lib/mysql/*; rm -fr /var/log/mysql/* 
/usr/bin/mariadb-install-db 1>/dev/null 2>&1 && echo OK
chown -R mysql:mysql /var/lib/mysql; chown -R mysql:mysql /var/log/mysql
systemctl start mariadb && echo OK

mariadb -ABNe "select version();"

mariadb -Ae "DROP SCHEMA IF EXISTS TBK; CREATE SCHEMA TBK;CREATE TABLE TBK.bktiming (c1 int(11) NOT NULL AUTO_INCREMENT,c2 datetime DEFAULT current_timestamp(),c3 varchar(100) DEFAULT NULL,PRIMARY KEY (c1)) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;CREATE TABLE TBK.thousand_rows (c1 int(11) NOT NULL, c2_ipsum varchar(500) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;CREATE USER 'mariabackup'@'localhost' IDENTIFIED BY 'mypassword'; GRANT RELOAD, PROCESS, LOCK TABLES, BINLOG MONITOR ON *.* TO 'mariabackup'@'localhost';"

mariadb -Ae "insert into TBK.bktiming(c3) values ('before any backup');"
rm -fr /var/mariadb; mkdir -p /var/mariadb
mariabackup --backup --user=mariabackup --password=mypassword --target-dir=/var/mariadb/full 1>/dev/null 2>&1 && echo OK
mariadb -Ae "insert into TBK.bktiming(c3) values ('after full backup');"
cat /var/mariadb/full/xtrabackup_checkpoints

# ADD 1,000 rows to a table, do it 100 times
for ii in {1..100}; do mariadb TBK < thousand_rows.sql; done;
mariadb TBK -ABNe "select format(count(*),0) as row_count from thousand_rows;"
mariadb -Ae "select (DATA_LENGTH+INDEX_LENGTH+DATA_FREE)/1024/1024 AS thousand_rows_IN_MB from information_schema.tables where table_schema='TBK' and table_name='thousand_rows';"

mariadb -Ae "insert into TBK.bktiming(c3) values ('before incremental backup');"
mariabackup --backup  --user=mariabackup --password=mypassword  --incremental-basedir=/var/mariadb/full  --target-dir=/var/mariadb/inc 1>/dev/null 2>&1 && echo OK
mariadb -Ae "insert into TBK.bktiming(c3) values ('after incremental backup');"

cat /var/mariadb/inc/xtrabackup_checkpoints