Explanation

This allows you to use a Python shell and Selenium to automate scrolling back through a teams chat and scrape the messages. The key variable is the position; each message has an attribute data-scroll-pos; the last/most recent message is at data-scroll-pos = 0. You can see this if you open the webtools and poke around, sometimes useful if the process gets borked and you're trying to restart it. The page is most likely to get refreshed if you or someone else who has access to the chat does something in teams, obviously posting a message in the chat will do it, but I suspect someone changing their status also might cause it. When this happens, the page will scroll back to the bottom again, and you have to use the scrollback_loop method to recover. To avoid this, best to run the process during off-peak hours.

Requirements

Python
Selenium for Python

To use:

in a console, cd to the chat-scrape directory
launch a Python interactive shell
in a browser, bring up teams and copy the url
in the console:
from chat_scrape import SeleniumScrape
ss = SeleniumScrape()
ss.session_setup("https://teams-url")
in the NEW browser that Selenium opened, log into teams, also bring up the chat you want to scrape
in the console:
ss.capture_setup("path-to/filename.txt")
ss.capture_loop()

Note that the capture loop will bork every so often. most of the time you can simply start it again
ss.capture_loop()
if the browser shows that teams has helpfully refreshed the page and you are now at the end of your chat history
you must run the scrollback. First take note of the last reported position, then
in the console:
ss.scrollback_setup(position)
ss.scrollback_loop()
Note that the scrollback loop may also bork, and hopefully will allow you to just restart it as well
Once the chat has scrolled back to where you left off, reset the position and restart the capture
ss.position = ss.target
ss.capture_loop()

If you want to scroll back to a certain date before starting the capture loop
in the console:
ss.scrollback_to_date(2021,3,2) #where the date you want to scroll to is 3/2/21

Note that manually scrolling around in the chat window may cause the position value to be invalid
where a valid value is a position that is currently visible or very close if that happens, you can either use the webtools to figure out a valid number or refresh the chat
and manually reset the position to 0 ss.position=0