I have had the exact same thing with a Samsung Galaxy Tab S8. You are right in that it's the web player builtin to the app that's causing you the issues.
Open Jellyfin app.
Select the menu Settingsunder the User header
Chose Client Settings
ChangeVideo player type to Internal player. Or use an external one, if you'd fancy that.
I've come to love the internal player very much, as in mt instantly loads the subtitles I choose to activate. The web player being slow and messy about it is my one big gripe with Jellyfin.
I always like to start over with a clean slate. The one that's been with me for about 15 years now is browser.tabs.closeWindowWithLastTab set to false.
I have had the exact same thing with a Samsung Galaxy Tab S8. You are right in that it's the web player builtin to the app that's causing you the issues.
I've come to love the internal player very much, as in mt instantly loads the subtitles I choose to activate. The web player being slow and messy about it is my one big gripe with Jellyfin.