1 Player Boardgames might be a better suit for you than Tabletop Wargames since those are usually not really designed with Solo play in mind. Plus Solo scenarios are more often than not just tacked on, dumbed down or meant as introduction/Tutorial to the game in order to prepare you for the "real" game against other humans.
That being said there's a few possibilities for playing solo which could be of interest to you. Since you expressed interest in Warhammer, there are solo scenarios and campaigns both homebrew and official for the current fantasy iteration Age of Sigmar. Here's a gameplay example on Youtube for one:
https://www.youtube.com/watch?v=ojq1YoDK8RE
Campaign Rules:
https://www.warhammer-community.com/wp-content/uploads/2020/04/~F5y~2bBG5-bJ~e2.pdf
https://www.warhammer-community.com/wp-content/uploads/2020/04/-jW22-Nj~Am44oF~.pdf
The Fallout wargame kinda blows IMHO, but the same company released an Elder Scrolls wargame based on the same but improved core mechanics. It's just personal taste but I still don't enjoy the systems. Might be worth looking into for you though since the Solo mode is featured somewhat prominently from what I understand:
https://www.modiphius.com/elder-scrolls.html
Something I would rather recommend to get started in Solo wargaming than those two games though is Frostgrave. It is a kinda lightweight but very fun wargame where you play a Wizard and his posse trying to get treasure essentially. It has a Rulebook explicitly for solo/coop play.
Core Rules:
https://ospreypublishing.com/frostgrave-second-edition
Solo/Coop expansion:
https://ospreypublishing.com/frostgrave-perilous-dark
Since Rangers of Shadow Deep was mentioned, a pulp spin in a similar vain is Perilous Tales:
http://planetsmashergames.com/perilous-tales/
A comparable Sci-Fi variant if you stretch it a bit would be Core Space:
https://shop.battlesystems.co.uk/core-space-starter-set-132-p.asp
Aside from this I would also strongly recommend you to look into Solo Boardgames. Since there are games specifically designed for Solo/Coop play I think you will enjoy them much more. There are even Solo boardgames that resemble wargames in the sense that they have miniature tactical combat/decisions. You can also save a ton of money if you don't care about the assembly and painting part by purchasing
https://store.steampowered.com/app/286160/Tabletop_Simulator/ many, many board games and some Tabletop Wargames (including your favorite Warhammer) are playable there (even Online, which might also help with the friends out of state/no friends issue). Rules for the games are usually downloadable legally and free from the games/publishers Websites.
Some solo boardgames worth looking into:
Zombicide, players against Zombies. Mostly get from A to B while killing/dodging zombies and looting gear along the way in either modern times (the first game), Fantasy (Zombicide: Black Plague) or Sci-Fi (Zombicide: Invader) setting. Personally I had most fun with Black Plague. Coincidentally you can also get that for free in the Tabletop Simulator Workshop.
If you like the video games you might also like the Fallout and Dark Souls boardgames (again both available for Tabletop Simulator). The Fallout one has story elements with choice and consequences but not a deep combat system. Dark Souls is kinda grindy.
For something completely different there's the Arkham Horror Deckbuilding card game (again Tabletop Simulator... I think you see a pattern emerging :D). You have 1 to 4 investigators built from class decks and must solve cosmic horror mysteries. Don't be discouraged by the label card game and give it a shot. It's really good.
Many people enjoy Gloomhaven, it's pretty deterministic though. There's a Steam version that supposedly will be faithful to the Boardgame.
There's also a Hellboy tactical boardgame haven't played that one yet though.
Other popular Solo Boardgames you could look into, albeit a little less what you are looking for yet popular for a reason are (and again many, if not all are available at the Tabletop Simulator Workshop):
https://tastybeansprout.github.io/SoloQuester/
/e: totally forgot to mention that Wargamers are usually a friendly bunch and you could always pay a visit to your local Hobby Shop if you are looking to play some Wargames with others. If you want to play Warhammer, the Games Workshop stores are your destination (just don't get talked into buying their super expensive paints ^^). A unaffiliated hobby store will offer a more diverse experience though since there are many, many interesting games other than Games Workshop products to be discovered and usually different hobby stores will have certain niche games on specific days aside from the currently universally popular Wargames (depending on their customer base's interests and local heroes who might organize and lure other regulars into "their" game).