I once exported my webflow project… changed all the .jpg to jpeg2000, and I saved a lot of speed.
You should also make sure your images are not to big, and if Webflow does not create a -500/800px image out of it, you could provide it yourself for mobile.
Not sure why Google ranks your page just 69 (in my test here), your images are not that large.
On my case studies pages the results are at like 75-85 or so (depending on the Google Insights mood I guess) for mobile only because of a helluva lot of gifs. But for a portfolio page it is understandible. If I were to remove the gifs the tests would score a solid 90 I think.
I think googles speedtest is a little too harsh. Your site is getting 89/100 with website.grader from Hubspot and 83/100 with Pingdom and that’s pretty good results.