Yes Muun does not work anymore. I would recommend Phoenix for you https://phoenix.acinq.co as better alternative.
In terms of HW if you look for a less expensive open source alternative try https://trezor.io
If you want to invest a bit more for your HW signer check out https: foundationdevices.com
Phoenix is non-custodial? If the app disappears you can load your private keys or seed phrase on any other App?
I heard bad things about Trezor too and Signer don’t are available on my country. I can’t afford a hardware wallet.
You can also start off with just a paper wallet for cold storage if you don't plan to transact day to day
Then as your stack increases in purchasing power you can grab a hardware device.
Also a tap signer might be a good choice too on a budget
