@jonasschnelli wrote in #14979:
> #14573 broke < Qt5.6 compatibility due to calling the lambda version of `addAction` that was added in Qt5.6.

We currently [support](https://github.com/bitcoin/bitcoin/blob/master/doc/dependencies.md) QT >=5.2, but hardly anyone tests with that. If we make one of the Travis machines use it, we should have a better change of catching this.

See also discussion about minimum QT version in #13478 
m_internals->m_schedulerClient.AddToProcessQueue([ptx, this] {
        m_internals->TransactionAddedToMempool(ptx);
    });
}
void CMainSignals::BlockConnected(const std::shared_ptr<const CBlock> &pblock, const CBlockIndex *pindex, const std::shared_ptr<const std::vector<CTransactionRef>>& pvtxConflicted) {
    m_internals->m_schedulerClient.AddToProcessQueue([pblock, pindex, pvtxConflicted, this] {
        m_internals->BlockConnected(pblock, pindex, *pvtxConflicted);
    });
}
void CMainSignals::BlockDisconnected(const std::shared_ptr<const CBlock> &pblock) {
    m_internals->m_schedulerClient.AddToProcessQueue([pblock, this] {
        m_internals->BlockDisconnected(pblock);
    });
}
void CMainSignals::ChainStateFlushed(const CBlockLocator &locator) {
    m_internals->m_schedulerClient.AddToProcessQueue([locator, this] {
        m_internals->ChainStateFlushed(locator);
    });
}
void CMainSignals::Broadcast(int64_t nBestBlockTime, CConnman* connman) {
    m_internals->Broadcast(nBestBlockTime, connman);
}
void CMainSignals::BlockChecked(const CBlock& block, const CValidationState& state) {
    m_internals->BlockChecked(block, state);
}
void CMainSignals::NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr<const CBlock> &block) {
    m_internals->NewPoWValidBlock(pindex, block);
}