Text message app keeps crashing

Well, what's the temperature that your iPhone is at when the apps crash (to the touch)? The iPhone processor works by doing short and intense bursts of high processing power but then have time to cool down in between. Your apps may be crashing due to having many apps open, if this is not the problem it could be your storage filling up. Also, try updating your phone to ios 14 if it isn't already. I really doubt that you have a virus (iPhone is one of the safest phones out there). Have you downloaded anything from your web browser lately or clicked on any links from unknown people messaging you in iMessage or in other messenger apps? Ok, final question, have you jailbroken your iPhone (highly not-recommended). Jailbreaking your iPhone takes away most of its security features.

If none of these solutions work then try restarting your iPhone.

if necessary try resetting all settings (I personally wouldn't do this unless really needed)