Have u tried this ? It does require your clips to be long enough so they don't get looped while transitioning.
Put clip 1 in layer 1 / column 1 , put clip 2 in layer 2 column 1.
On clip 1 , go to the clip opacity parameter, click the gear icon left of it and choose "Clip position"
Now the opacity value will go from 0 to 100% over the duration of the clip.
Click the gear icon again, enable Enveloppe , and reverse the enveloppe line so it goes from 100 to 0%
Do the same for clip 2 but let the enveloppe be from 0-100%
If you now start the clips by pressing on the column 1 tab, it should work, and u can use the enveloppes to fine tune the duration and curve of transition.
That said, it would be nice to be able to add a custom big number in the layer transition parameter (havent tried if it can yet to be fair). Just leave the slider next the layer transport controls on 10s pls so i don't accidentally scroll over it & put it on 2000sec