There are plenty of calendar apps that do repeating alerts (so you get a popup but it will repeat every minute). I'm currently using aCalendar+ this way, I know Business Calendar 2 does it too. Nine (purely a paid app, has a trial period but no free version) has a "persistent alert" setting, i.e. continues to make a sound until you dismiss it. I can't answer for the Outlook app because I don't use it myself.
I used to use an app called "Calendar Snooze" for this, which was perfect for me: full-screen alerts, flexible snooze options, everything my old Palm devices gave me, and would handle the notifications whichever calendar app I used (allowing me to try different calendar apps without compromising on the notifications). Unfortunately it's no longer supported: if you have an old enough phone it may still work, but if you are on Android 9 or 10 you are probably out of luck. But maybe there will be a "similar app" in the play store that does something similar (the alternative I'd tried a year ago no longer exists, so there isn't one I can recommend from experience).