After the free trial expired and NOT purchasing Sketchup 2019, I can no longer open older files created with 2017 - 2018. Any thoughts? Thank you!
You could try Eneroth’s Open Newer Version extension: https://extensions.sketchup.com/en/content/eneroth-open-newer-version
If you saved the files in SU2019 they are no longer older files. You could upload them to the 3D Warehouse and then open them in SU2017 or you could open them with SketchUp Free. Your profile and the category you selected for this post are confusing.
I didn’t realize that the web version now also accepts / runs extensions.
the web ‘versions’ will open all versions of .skp…
some my take ‘forever’ or the OP may be referring to Make…
Obviously it doesn’t. But I had assumed that the OP had likely gone back to Make, which would.