pg_upgrade from 18beta1 -> 18beta3 - problem with btree_gist contrib module / extension

pg_restore: from TOC entry 4295; 1255 596569951 FUNCTION 
gist_stratnum_btree(integer) postgres
pg_restore: error: could not execute query: ERROR:  could not find 
function "gist_stratnum_btree" in file "/usr/local/pgsql/lib/btree_gist.so"
Command was: CREATE FUNCTION "public"."gist_stratnum_btree"(integer) 
RETURNS smallint
    LANGUAGE "c" IMMUTABLE STRICT PARALLEL SAFE
    AS '$libdir/btree_gist', 'gist_stratnum_btree';


The solution was to somehow restart 18beta1, drop btree_gist and all its 
dependent constraints / indexes / objects , pg_upgrade and finally 
re-create extension and dependent objects.