is replication effected by exclusive locks?

hello - first a thank-you to this list for all previous questions answered
here!

In our cluster, we're using read-only replicas for answering postgis geo
queries. Often, i see multiple queries coming in concurrently & regularly
taking 2-10 seconds. When looking closer at these queries, i see they all
use an ExclusiveLock.

And when this is the query traffic, there can be increasing replication lag.
But also - there can be waves of tx cancellation due to conflicts, ie.
replication.

note that in this setup, pg_vacuum_defer_cleanup_age = 0 so the cancels
make sense to me.

So the simple question: do ExclusiveLock compete or block application of
wal logs on read replicas?

thanks in advance for thoughts/tips/links/etc