That v44 lipo cell has a built in solar charge controller and has always-on capability, though it looks like there are some voltage limitations (you can’t plug a 12V or 18V solar panel in; all their panels are 6V or so). FYI you could probably get away with a smaller panel (the Watt-hour consumption of the Gotenna is pretty low).
One of the other options would be to get a dedicated solar charge controller with a separate lithium battery but I think the v44 solution is cleaner. This list was what I came up with before I noticed the v44 has this amazing feature. AGM batteries are cheaper but if they get discharged they completely shit the bed after a relatively short amount of time. The key advantage (and why people probably select them) is that there are a lot of solar charge controllers available for the 12V AGM voltage levels; lithium batteries have different voltage and charging characteristics and may explode if used with a regular 12V RV style charge controller. The charge controller in that shopping list is specifically modified for lithium use in the 3 cell configuration which is something like 11V nominal. From what I can tell that charge controller has minimal no-current draw with the integrated USB ports, but if you grab a cheap 12V to USB adapter off the internet they are likely to be pretty inefficient like just dumping the extra voltage with a regulator instead of using a higher quality DC-DC converter with the storage elements required to drop noise to an acceptable level.
I believe the OmniCharge battery packs have something similar (they can disable the auto-off), but one of the key things is that the v44 in “Always on” mode will shut off on a low battery power condition and then restart without intervention once enough solar has come in – I’m not sure how OmniCharge handles that. Not to mention the v44 is cheaper.