There is also TN-Grid and SiDock but they are still getting there next lot of work organized and have no work at the moment.

Step 1: Use a recent BOINC version (partially due to bundled Internet certificates; older BOINC will have older certificates, and some may have expired by now). As of this post, the most recent version is 8.2.1. (Note: The oldest device I have running 8.2.1 is an Android 9 Phone; it's the oldest device overall that I have. For tablets, I have one, running Android 15.)
Step 2: Use the 3-dot drop-down menu next to the '+' option; you should see an "Add by URL" option. (The "+", 'obviously', pulls from the preset list.)
Step 3: In the 'main' settings (you MIGHT need to select "Show Advanced Settings" to make this appear), select the RPC option; this way tasks will validate. (Otherwise they'll run and return, but won't validate - it won't recognize any hours from the other projects you are running at the same time.)

I talked to the people who sold them & they agreed to give me a 50% refund

they were shipped from China