I am running PSE2018 fully updated. Just switched from Canon 70d to 90d, with the new CR3 RAW format. Adobe lists this as a supported format, but it doesn't work on my software. Any suggestions? Thanks.
As you can see from the two links in that faq, your 90D requires ACR 11.4 and PSE2018 can't be updated to more than 11.3.
The free solution in your case is to download the free Adobe DNGconverter mentioned in the faq.
That independent tool (not a plugin) will batchconvert a whole folder of your CR3 files to the DNG raw format that your PSE version can read and edit. An additional batch operation, but free and with the same quality.