OK, I got 6.70 to work but not using @Laxus version so you dont get the cheat options included, just the igg memory engine and other tools menu. Also, I used the 0.8.3 deb file as that was the last one that worked for me.
You can download the decrypted ipa from here >. https://armconverter.com/store/us/csr racing 2
Drop it into Sideloadly
Add the 0.8.3 deb file
Select 'Advanced Options'
Click on the 'Dropping 0 of 2 plug-ins' box and select 'Extensions/BckgroundDownloadExtension.appex' and click OK
It should now say 'Dropping 1 of 2 plug-ins'
I always have 'Enabled File Sharing' checked but not sure if this makes a difference here
Click 'Start' and hopefully it works for you too.
@Laxus let me know if not appropriate to put this post in here as I don't want to hijack all your great work over the years