First thing I think is to set your expectation. It'll be very hard to completely abandon iOS/Android. I managed to only use UT for around 5 years but had to have an Android phone as secondary phone in the past few years. Some things are just not possible on UT. There's Waydroid to try some apps that you need but not all will work especially those that needs security checks and such. Waydroid also drains the battery.

X and Proton Mail can only be accessed via the browser/webapp. Proton mail doesn't support the usual email configs (IMAP/SMTP) so you can't use Dekko. There are a few Reddit clients in the store though not sure how good they are compared to just using the web version.

We currently only have Morph as the browser with Sapot browser as a fork with a bit different UI but still the same web engine which is sadly outdated right now due to technicalities.