Referencing joined table loading every time

Hello - are you performing the join as a new query or within an existing query?  Joining as a new query should solve this problem.  When the join is done within an existing query (the join is not the first step in the query), a separate call to the source is made for each row.  I have included a link where this is explained in more detail.

https://docs.microsoft.com/en-us/power-query/optimize-expanding-table-columns#:~:text=When%20queries%20reach%20this%20bottleneck%2C%20the%20best%20mitigation,using%20the%20common%20key%20between%20the%20two%20tables.