Apprecaite your help on this.
It sounds like there might be a mismatch in the source for the dashboard where you are trying to chart these measures. If you have made the measures, once you select the right system profile you should be able to chart them without an issue. I would suggest opening a blank dashboard, checking the source for that dashboard (in the screenshot below) and then selecting use for analysis then charting. Once there, you should be able to add the series that you want to track in that chart.
Below I am showing my source as the Dynatrace Self Monitoring system profile and since this is not an application based system profile the browser measures do not show up when I try to add measures to the chart.
Browser Side measures are only available when you use a browser agent. The browser agent is no longer supported, and I am guessing you are not running one. If you have User Experience Management (UEM) enabled and working, you should be able to see Visits and User Actions (under Diagnose User Experience) and get measures from UEM that are similar to the Browser agent measures.