Old LR classic won't read own catalog, then keywords vanish after update to Lightroom Classic 11.1

I have just been working with 3000 photos taken on recent trip (a lot of birds and animals and a few people).

(1) In a possibly misguided attempt to keep things simple while I worked on them, I created a new catalog just for these photos rather than insert them into a very large catalog of 20 years.  I created an elaborate structured set of keywords and applied one or more keywords to each of the 3000 photos.   I was using an older version of Lightroom, the last one that would work with Mac High Sierra.  After doing a lot of work, I decided to quit LR Classic for a little while with the idea of backing some things up.  But when I tried to open the catalog, LR said the catalog was too modern to open even though it was the very same copy of LR  that created it.  THIS MADE ME SORT OF CRAZY but I tried to calm down.

(2) In an attempt to rescue my work, I updated my old Mac Mini to Catalina and updated LR Classic to 11.1. When I opened the catalog, LR updated the catalog.  They phots are still there and some star ratings but my set of keywords was replaced by some weird subset and almost no keywords were applied to invidual photos.  Also all the Stacks had disappeared.  Also all the Smart Collections based on the vanished keywords.  What kind of update is this?

So, is there any way to get my work back?  

(3) Worse yet, I am afraied to open my big catalor with tens of thousands of edited and keyworded photos.  What will Version 11.1 do to this older catalog?  Is there any way to protect the metadata there now (if I can somehow retrieve an old copy of LR Classit to open the old catalog with?

I am scared of losing years of work.