I found it. More steps then is used to be and it has a 500 item selection limit. Layers can have more than 500 items, but the function I found only selects 500 items on a layer at a time.
Here goes: Show the layer tree in the left panel Right click on a layer (or select the layer and then right click) for a fly out menu Select "Select Items" on the fly out menu all the items on the layer (up to 500) will be selected Go to the "Edit" menu in the top menu and select Suppress
Alternatively, you can expand the layer name in the layer tree and Select the first item in the layer item list, scroll done to the bottom of that list and, while holding down the control button, select the last item in that layers list. Then go to the edit menu and select "suppress. There is still a 500 item limit, but after you've suppressed the first 500 items you can repeat the process to select and suppress more items.
A bit more cumbersome than it used to be, but it works.
So why do I have more than 500 items to suppress? Our electrical group uses Altium to create curcuit boards. They output the 3D step files. When I bring those files into proe as an assembly, they often have several hundred to several thousand parts. Most of them are tiny little blocks that I don't need. The bigger parts and jacks I need to see to fit housings around. I put the big parts on a layer and do the same with the little parts. Then, to keep the session from loading thousands of part names into session I suppress the little parts. It's very tedious to find a part in session when you have to scroll through a list of over a thousand parts.
Often times I will suppress all but the little parts so that only the little parts are shoiwing. Then I output that as a step or .sat file and bring that back into one part called "lil parts". I delete the little parts from the assy and bring in the one part file that has all the blocks from the little parts. Then I can see them all but they are just one part name in session.