Why do I need multiple active portals????

[tamis-laan]

Given the following approximate code:

async with db.acquire() as conn:
    async with conn.transaction():

        id = await conn.fetchval("UPSERT INTO .... (..., ...) VALUES ($1, $2) RETURNING id", C, D)

        for A in my_list:
            await conn.execute("UPSERT INTO ....  (..., ....) VALUES ($1, $2)", A, id)

I get:

asyncpg.exceptions.FeatureNotSupportedError: unimplemented: multiple active portals is in preview, please set session variable multiple_active_portals_enabled to true to enable them
DETAIL:  cannot perform operation sql.PrepareStmt while a different portal is open
HINT:  You have attempted to use a feature that is not yet implemented.
See: https://go.crdb.dev/issue-v/40195/v23.1

Which I don't understand. Why do I need "multiple active portals" in this case? I'm using cockroachdb.