I love FOSS and hate myself for doing this but personally I gave up on the idea of forcing myself to using a worse FOSS app over one that just get's "shit done".
Convenience in the gym is the most important imo.
Hevy is a great app even without paying. Take that for what you will.
Have not tried it but came across this some time ago. https://github.com/guysoft/FullPageOS