Garmin Explore has a bit of a learning curve but offers a variety of very good maps and (once you’ve discovered where the web developers have hidden them) tons of nifty features. One of them is waypoints: you stick a flag somewhere and can give it a name, icon and colour. That sounds like the thing you’re looking for.
The downside is that it’s made for outdoor stuff so you get street names and some POIs, but no turn-by-turn navigation.

I use the website (https://explore.garmin.com/) to plan my tours and import/manage GPX files, and the Android app and an inReach 2 Mini satellite messenger while underway. The three sync seamlessly.

Since I have a paid subscription (required for satellite access) I can’t tell you what (if anything) you get for free, but it should be relatively easy to find out if you think it might be what you’re looking for.

For car navigation I used TomTom Go - it costs something but the quality of POIs and navigation is far superior to Google Maps in my experience. You can also add your own locations but have to do it on the phone by hand.
In my new car I use Google Maps because it came with the car and there’s no real alternative at the moment. I do miss my TomTom app.

That screenshot alone brings back so, so many memories.

Been with Winamp ever since my first 486DX all the way up to my first 4k screen when it became unusable due to size/scaling issues.

I’m really keeping my fingers crossed for this one to succeed.

There’s actually an option to turn GMS off entirely if that’s a concern (Settings–>About–>Advanced). It comes at the cost of slightly increased battery usage. Sadly Google does have a bit of a monopoly on mainstream Android there.
Having said that, the messages themselves should never pass Google’s servers, just a packet saying “check your Threema server, there’s new stuff waiting for you.”

If that’s a concern you could also always use Threema, which has been built from the ground up to use anonymous random IDs and optionally lets you link a phone number or e-mail address to that ID. The company has also won important court cases against having to store metadata preemptively and responding to blanket requests by law enforcement.

I use VLC for the handful of streams I need regularly. In the More tab you can create launcher (home screen) shortcuts for recently viewed streams and then rearrange them into a group. It doesn’t get any more straightforward than that.

I see several issues with your SMTP session.

First, gmail.com will be protected by SPF and DKIM and your message will likely be flagged as spam (or outright rejected) because it’s clear that you’re not sending on behalf of the real gmail.com.

Second, commands should be in all-caps. A server may accept or reject lowercase keywords.

Third, you need to leave a blank line between the mail headers and the body, so that part of your session would look like so: …

DATA
354 Go ahead
From: ...
To: ...
Subject: ...

This is the first line of text.
This is the second line.
.
250 Queued

Having said that, many servers will require an encrypted connection (SMTPS), many ISPs will block port 25 for residential customers as an anti-spam measure (so your local mail server may accept the message from your script but be unable to forward it), ESMTP should be preferred over SMTP etc.
If at all possible, you should use a full-featured mail library for this and use your ISP’s own mail server.

Doesn’t Pop_OS come with a sendmail command?

No specific suggestions, but sort of a half-anti-recommendation:

I used to own a Tolino Vision 2. It was a great device for its purpose and time - lightweight, sturdy, very pleasant e-ink screen and backlight, easy to use and didn’t mind a little sand or water. Sadly I lost it.
The new models I could try out look even nicer, but they all share one common problem: half of the home screen is an online book shop that can’t be changed or hidden. That was reason enough for me not to buy another one.
If you don’t mind that and Tolino devices are available where you live, they may be worth a try. Otherwise I recommend you steer clear of them.

As for the DRM issue, de-DRMing with Calibre for some reason didn’t work for me (quite possibly a wetware problem), so I ended up buying ePubor Ultimate, which works very well and can do a lot of things but isn’t free.

I wasn’t aware of the CloudFlare thing, thanks. Though I’d trust them more than Google or Meta, I share your reservations. Looking at how big a part of the web they serve, there’s already way too much power in too few hands anyway.

That app was revolutionary for its time and a true life-saver. (For the young ones: at a time where mobile networks were still really, really slow, Opera’s technology would load the requested web page on its server farm, parse it, strip out the unnecessary stuff and send it to your phone in a highly compressed form. It basically enabled you to surf ‘normal’ web pages without overloading your phone and with load times measured in seconds instead of minutes.)

ISTR news/discussions where several shady companies were said to want to buy Opera for that technology, for the simple fact that everything you did on Opera Mobile was at some point processed on Opera’s servers in unencrypted form. I dread the day where Google or Meta start offering such a service.

Long-time Opera user here (I paid for Opera 5 - yes, that long ago). Opera was a truly visionary browser up to version 7 or so based on its own Presto engine, but nowadays it’s just another Chrome clone with dubious features IMHO.

Opera’s successor in spirit is probably Vivaldi. I use it as my standard browser on Windows and Android and am very very happy.

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FX File Explorer has that functionality (among other cleanup tools) and is generally a great file manager. It’s free with limited functionality after a trial period, or a one-off fee of about three bucks for the Plus version.