Personally, i would use VPN, Pihole for Local-DNS Records and a simple Local Reverse Proxy to address my Network-Services. I wouldnt open anything from my Homelab to the Internet.

I am using the same i use for my Smartphone. Fairbuds XL via Bluetooth.

No Problem :)

I think there is an APP for all major Plattforms (Desktop and Mobile):

https://stoat.chat/download

iOS and Android are listed.

Or what do you mean with mobile client?

Maybe Stoat/Revolt is for you. Stoat has - in my opinion - the same look and feel as discord.

It is OpenSource, selfhostable and it comes with most features discord has - excluding nitro.

There is an Android, Linux and Windows APP.

You could check for Linux support. I suppose it runs on an Arm-Processor.

Maybe it runs PostmarketOs.

Edit: If you can run Linux on it:

Selfhosted:

• Gitea (If you are a programmer)
• Stash (Organized NSFW-Content ( ͡° ͜ʖ ͡°) )
• Nextcloud
• Simple-Server ( NAS/SFTP/SSH)
• MeTube (Youtube-Downloader)
• Kitchenowl/Mealie (Kitchen-Organization / Mealprep)
• Lute (Selfhosted Alternative to Duolingo)
• Speedtest (Monitoring Internet-Speed)
• wishlist
• Hortusfox (For managing your Plants)
• MotionEye (Security-Cam-Monitoring)

On-Device:

• Libreelec/Kodi (Media-Device)
• Retroarch (Retro-Gaming-Station)