Server crash on converting table to utf8mb3

CREATE TABLE t (c TEXT,PRIMARY KEY(c (768))) ENGINE=InnoDB;

INSERT INTO t VALUES (100);

ALTER TABLE t CONVERT TO CHARACTER SET utf8mb3;

SELECT 1 FROM t GROUP BY @b :=@a,@b;

mysqld: ../storage/innobase/dict/dict0dict.cc:2322: dict_index_t *dict_index_build_internal_clust(dict_index_t *): Assertion `!index->has_virtual()' failed.

210624 20:29:01 [ERROR] mysqld got signal 6 ;

This could be because you hit a bug. It is also possible that this binary

or one of the libraries it was linked against is corrupt, improperly built,

or misconfigured. This error can also be caused by malfunctioning hardware.

To report this bug, see https://mariadb.com/kb/en/reporting-bugs

We will try our best to scrape up some info that will hopefully help

diagnose the problem, but since we have already crashed, 

something is definitely wrong and this may fail.

Server version: 10.4.20-MariaDB-debug-log

key_buffer_size=1048576

read_buffer_size=131072

max_used_connections=1

max_threads=153

thread_count=3

It is possible that mysqld could use up to 

key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 63650 K  bytes of memory

Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x7fca30001618

Attempting backtrace. You can use the following information to find out

where mysqld died. If you see no messages after this, something went

terribly wrong...

stack_bottom = 0x7fca440f8d50 thread_stack 0x49000

mysys/stacktrace.c:174(my_print_stacktrace)[0x56432441a47b]

sql/signal_handler.cc:222(handle_fatal_signal)[0x564323994624]

/usr/lib/libpthread.so.0(+0x13960)[0x7fca5422d960]

:0(__GI_raise)[0x7fca53e8bef5]

:0(__GI_abort)[0x7fca53e75862]

loadmsgcat.c:0(_nl_load_domain.cold)[0x7fca53e75747]

:0(__GI___assert_fail)[0x7fca53e84646]

/home/nik/mariadb/bld/sql/mysqld(+0x13dcab4)[0x5643240a3ab4]

dict/dict0dict.cc:2322(dict_index_build_internal_clust(dict_index_t*))[0x5643240a2a70]

dict/dict0crea.cc:1249(dict_create_index_step(que_thr_t*))[0x56432408f488]

que/que0que.cc:1048(que_thr_step(que_thr_t*))[0x564323e0aa94]

que/que0que.cc:1100(que_run_threads_low(que_thr_t*))[0x564323e099d5]

que/que0que.cc:1142(que_run_threads(que_thr_t*))[0x564323e096ed]

row/row0mysql.cc:2560(row_create_index_for_mysql(dict_index_t*, trx_t*, unsigned long const*))[0x564323e8ed07]

handler/ha_innodb.cc:11371(create_index(trx_t*, TABLE const*, dict_table_t*, unsigned int))[0x564323ca56ec]

handler/ha_innodb.cc:12454(create_table_info_t::create_table(bool))[0x564323c816ba]

handler/ha_innodb.cc:12975(ha_innobase::create(char const*, TABLE*, HA_CREATE_INFO*, bool, trx_t*))[0x564323ca696f]

handler/ha_innodb.cc:13026(ha_innobase::create(char const*, TABLE*, HA_CREATE_INFO*))[0x564323c8307f]

addr2line: DWARF error: could not find variable specification at offset 8445

sql/handler.cc:4790(handler::ha_create(char const*, TABLE*, HA_CREATE_INFO*))[0x5643239a75ad]

sql/handler.cc:5255(ha_create_table(THD*, char const*, char const*, char const*, HA_CREATE_INFO*, st_mysql_const_unsigned_lex_string*))[0x5643239a92be]

sql/sql_table.cc:10308(mysql_alter_table(THD*, st_mysql_const_lex_string const*, st_mysql_const_lex_string const*, HA_CREATE_INFO*, TABLE_LIST*, Alter_info*, unsigned int, st_order*, bool))[0x5643236abf91]

sql/sql_alter.cc:520(Sql_cmd_alter_table::execute(THD*))[0x56432376ebd7]

sql/sql_parse.cc:6189(mysql_execute_command(THD*))[0x564323591b56]

sql/sql_parse.cc:7992(mysql_parse(THD*, char*, unsigned int, Parser_state*, bool, bool))[0x56432357d284]

sql/sql_parse.cc:1857(dispatch_command(enum_server_command, THD*, char*, unsigned int, bool, bool))[0x56432357945e]

sql/sql_parse.cc:1373(do_command(THD*))[0x56432357e2a4]

sql/sql_connect.cc:1412(do_handle_one_connection(CONNECT*))[0x564323763014]

sql/sql_connect.cc:1316(handle_one_connection)[0x564323762dca]

perfschema/pfs.cc:1869(pfs_spawn_thread)[0x564324387a05]

pthread_create.c:0(start_thread)[0x7fca54223299]

:0(__GI___clone)[0x7fca53f4e053]