MySQL:

ST_GEOMETRYN

ST_GeometryN(gc, N)

Returns the N-th geometry in the GeometryCollection value gc.
Geometries are numbered beginning with 1.

ST_GeometryN() handles its arguments as described in the introduction
to this section.

URL: https://dev.mysql.com/doc/refman/8.0/en/gis-geometrycollection-property-functions.html

Example

mysql> SET @gc = 'GeometryCollection(Point(1 1),LineString(2 2, 3 3))';
mysql> SELECT ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1));
+-------------------------------------------------+
| ST_AsText(ST_GeometryN(ST_GeomFromText(@gc),1)) |
+-------------------------------------------------+
| POINT(1 1) |
+-------------------------------------------------+