We bundle the StreamFX plugin to provide additional encoders in OBS. This plugin does not play well with some (very) old CPUs. If OBS will not open for you, open a terminal and try the following:
sudo mv StreamFX.so /tmp/
Then try to launch OBS. If this works you will need to do this when you launch OBS until the issue is resolved and/or we remove the plugin in a future update (or until you upgrade your CPU).