Curious. Touch portal is working fine for me.
I tried the Steam Deck mobile app on my iPhone and was not impressed.
I have an iPad Air that was gathering dust. I looked at both Metagrid and Touch Portal. And decided on Touch Portal for three reasons. Like you said, the version of Metagrid that would run on my iPad is not the version which will be developed going forward. And only Touch Portal had a trial version. And finally, Touch Portal was cheaper.
I have had to restart Touch Portal on my Mac on occasion to get the devices to communicate with each other. But this is rare.
So far I’ve been happy with Touch Portal. Bummer that it didn’t work for you.
Good luck in your search.