If setting the "BrowserSignIn" managed configuration parameter of Chrome "com.android.chrome" browser app in your MobiControl App policy cannot solve your problem, then whitelisting in either ARC or kiosk policy your mentioned activity "'com.android.chrome/org.chromium.chrome.browser.firstrun.FirstRunActivity"  is one possible solution.

No but you can check Chrome app config if you casn disable it there.

I assume you are trying to use feature called Chrome Custom Tabs (CCT). There is Chrome managed config parameter called "Configuring the ToS behaviour during first-run for CCT" you need to configure to "Automatically skip ToS ..." bud also whitelist Chrome itself in Lockdown without showing app icon for it - this is tricky and you need to customise Lockdown template based on your requirements.

Another possible workaround would be to have some staging group with lockdown that have Chrome added fully to Lockdown and run your CCT app once there so it would launch and skip the ToS screen (you don't need to do it manually it just pops out and close itself once but if Chrome is not whitelisted it won't work) you've configured using managed app policy and move device to different group with Lockdown without Chrome.