Element 2019 stoped!

I'm not going to berate Apple for this, as I'm not smart enough to challenge decisions they make on engineering levels but, it at least seems plausable to me they could have built some backward compatibility into Catalina but decided not to.  I'll only say that my standard fare 64 bit Windows 10, running on a 64 bit Intel CPU processor (a rather plain vanilla setup) runs PSE 2019 beautifully and it seems odd that Macs aren't able to do so as well.  Maybe someone much smarter than me can explain.  I feel bad for you, Marie but you're pretty much stuck with upgrading to PSE 2020 or doing without.     

Can you open it by right clicking on a photo and clicking open with?

Was this sudden behavior preceeded by any upgrades/updates to your OS?  Which platform do you use?