Installing APEX 20.1 on Oracle 19.3 - oracle

Question

When installing APEX, I get the following error from Phase II of the installation procedure. I have no idea why: Many thanks for any hints
ok 1 - BEGIN | 0.00
ok 2 - Upgrade Metadata (1) | 0.00
ok 3 - Init Phase PRE | 0.03
ok 4 - Dropping Upgrade Triggers in FLOWS_020100 | 0.00
ok 5 - Creating Upgrade Triggers | 0.00
ok 6 - Incrementing Session Sequence | 0.00
ok 7 - Disabling Constraints/Triggers | 0.02
ok 8 - Copying WWV_FLOWS | 0.07
# copied 2 rows into WWV_FLOWS
ok 9 - Rebuilding WWV_FLOWS_IDX_AUTHENTICATION | 0.00
not ok 10 - Copying WWV_FLOW_BANNER | 0.00
# Message: ORA-06550: line 6, column 14:
# PL/SQL: ORA-00932: inconsistent datatypes: expected CLOB got LONG
# Statement: begin
# insert /+append/ into "APEX_200100"."WWV_FLOW_BANNER"
# ( ID,
# BANNER,
# SECURITY_GROUP_ID)
# select ID, BANNER, SECURITY_GROUP_ID
# from "FLOWS_020100"."WWV_FLOW_BANNER" bt1
# where security_group_id not in (10, 12) order by SECURITY_GROUP_ID ;
# wwv_flow_upgrade.g_row_cnt := sql%rowcount;
# end;

Answer 1

it appears that the 19.3 database already contained a super-old APEX version (HTML DB 2.1). When the APEX installation detects an existing APEX version, it attempts an upgrade.
And in the meantime (HTML DB 2.1) is about 15 years old, there were some major changes which break this large upgrade jump from 2.1 to 20.1.
The most important question is ...
Is that existing HTML DB 2.1 installation in use or not? If not, simply drop the FLOWS_020100, FLOWS_FILES and FLOWS_PUBLIC_USER database users and re-attempt the installation.