I tested the upgrade locally to J6 and wanted to share it with you.
The system asks me to disable the BC plugin. Once disabled, the front end wasn't visible.
However, the back end continued to work. I upgraded to J6 anyway, and everything went well. The front end is now visible correctly.
Before proceeding, please update JA ACM, JA Extension Manager, and JA Masthead.
In my case, the template used for the test is JA Trip and it seems to works despite it didn't receive any update for J6.
I have a little more faith in Joomlart for the future. However, I must say that most of us signed up in 2017/2018. And obviously, we have works around based on T3. And what I think are the best Joomlart templates are based on T3.
Please @saguaros make sure these templates are also upgradeable to J6.
And go back to being number one on the market.
We will remain loyal customers if you proceed in this way.