Monthly percentage change from a fixed point in time, based on a Slicer Selected month

[N_R_000]

I'd like to create something like the below, which shows the % change of something when compared to a single point in time. 

I know I can easily show 'month on month' % changes, but I'd like to show how the % changes look every month when that month is compared to a selected month in the past.  

I've had to sanitise the data a bit, but here's what I've got - a date table and an events table. Many events happen each day, so I'll need a COUNT for the 'Base Month' then a measure to take each subsequent month and compare to the Base Month to get the % change. I'd like to lines on the chart, one for each 'Event Type'.  The X axis will be 'Start of Month', the other axis will be '% Change'. 

I'd really like the 'Base Month' to be set by a slicer so the user can update this, but if that's not possible, I'm happy to hard code a date in DAX as plan b.  

[Dates]				[Events]
Date	FirstOfMonth			EventID	Date	EventType
01/01/2023	01/01/2023			1	01/01/2023	Minor
02/01/2023	01/01/2023			2	01/01/2023	Major
03/01/2023	01/01/2023			3	01/01/2023	Minor
04/01/2023	01/01/2023			4	05/01/2023	Major
05/01/2023	01/01/2023			5	05/01/2023	Minor
06/01/2023	01/01/2023			6	05/01/2023	Major
07/01/2023	01/01/2023			7	05/01/2023	Major
08/01/2023	01/01/2023			8	09/01/2023	Minor
09/01/2023	01/01/2023			9	09/01/2023	Major
10/01/2023	01/01/2023			10	09/01/2023	Major
11/01/2023	01/01/2023			11	12/01/2023	Minor
12/01/2023	01/01/2023			12	12/01/2023	Minor

These dates and events continue up to today, I've just truncated the data for this post. 

I've spent a day trying to get ChatGPT to help with DAX with no luck, so here's hoping the human commnuity can come to my aid! 

Thanks. 

[lbendlin]

Please indicate the expected outcome based on your sample data - or provide more covering sample data.