Elkin What will happen with the additional patches that bnestere and knielsen discussed/proposed? Also, where does this leave MDEV-31949/ MENT-1905?

Roel, that code is currently in Kristian's branch. I thought the best place for it would be 11.5, as a polished version of this bug fixes.
MDEV-31949 keeps aiming to 11.6.

Elkin Ack, thank you. Should a new ticket be created for those patches? As they will require testing, I think we should look at 11.6 for those as well.
Also, is this patch (MDEV-33668 inc the additional patches) fully compatible with MDEV-31949?

Roel, a new ticket, of course. I'll report one when have fully understood its merge with MDEV-31949. The latter is different on the slave side, maybe the merge with this solution will lessen that, and 31949 also refines the master side because of recovery (MDEV-21777, MDEV-32830).

From the list above (all bugs reproduced in BASE as well, except #6 ftm):

1. [ERROR] Slave SQL: Commit failed due to failure of an earlier commit on which this one depends, Gtid 0-1-20, Internal MariaDB error code: 1964 (and variations thereof)
> This is now MDEV-34010

2. [ERROR] Slave I/O: Got fatal error 1236 from master when reading data from binary log: 'could not find next log; the first event '.' at 4, the last event read from 'binlog.000009' at 2595, the last byte read from 'binlog.000009' at 2702.', Internal MariaDB error code: 1236 (and variations thereof)
> Filtered after analysis

3. [ERROR] Slave SQL: Error executing row event: 'You can't combine write-locking of system tables with other tables or lock types', Gtid 0-15-143, Internal MariaDB error code: 1428 (and variations thereof)
> This is now MDEV-34011

4. [Warning] Slave: Got error 140 "Wrong create options" from storage engine InnoDB Error_code: 1030 (w/ slave halt). This one may be XA related.
> This is now MDEV-33961

5. (Slave Crash) SIGSEGV|dict_table_t::is_active_ddl|trx_t::rollback_low|trx_t::rollback|trx_rollback_last_sql_stat_for_mysql
> This is now MDEV-34051

6. (Slave Assertion) thd->transaction->stmt.is_empty() || thd->in_sub_stmt || (thd->state_flags & Open_tables_state::BACKUPS_AVAIL)|SIGABRT|close_thread_tables|mysql_execute_command|mysql_parse|Query_log_event::do_apply_event
> Ref MDEV-32372

7. !look_for_rollover || start_scan_slot != slot|SIGABRT|trx_assign_rseg_low|trx_start_low|trx_start_if_not_started_xa_low|create_table_info_t::create_foreign_keys and
!look_for_rollover || start_scan_slot != slot|SIGABRT|trx_assign_rseg_low|trx_start_low|trx_start_internal_low|dict_stats_fetch_from_ps
> This is now MDEV-33917

This comment will be updated as work on bugs progresses is now complete.