I'd just use AD&D; if I wanted a more "modern" approach, Castles and Crusades.

Every time I want to run a new fantasy campaign, I always look for alternatives to AD&D and C&C and find all sorts of neat stuff about a variety of systems I think is cool and waste a ton of time trying to figure out how to use those systems, then end up back where I started and just play C&C.  Yeah, it has issues, but if you want to PLAY an RPG, it works fine. I am sure you can find plenty of alternative character classes out there. I have all the published codexes (codices?) and there is enough variation to last forever.

Through Sunken Lands might be an interesting option, though. Hyperborea looks cool but ehhh...and WWN is absolutely cool, but not strictly fantasy, honestly.

Nimble 5E is a new game based on 5E , but redesigned to make gameplay faster. 

It uses the damage roll as the hit roll, with a 1 as a miss, and max damage as a crit. 

Each level gives a good ability, so no "dead" levels.

Initiative determines how many actions/reactions you get for the round. 

5e - I still run 5e. PHB 2014, And I limit the classes/races for each campaign. I use some homebrew and some 3rd party stuff that is specific to the campaign that I am running. Number of house rules that I have collected over the years. It works and for some of my groups it is the best system for them.
 
Level Up: Advanced 5th. Edition - I own it. I really wanted to like it. But it just didnt hit right. It reads like it would be great, but in play it ended up just feeling like a weird hybrid of 5e and Pathfinder. My recommendation if that if you think you might like A5e would be to play Pathfinder 2e instead. You'll feel better about the money you spent. It was not however a complete loss. The A5e Monster Manual is easily the best 5e monster book on the market. I've also stolen some of the rules for my 5e game, but I would not recommend picking up the rule books just to do that.

Castles & Crusades - What 3e should have been. I personally love it and it works great for running all of my old 2e material I have kicking around. A number of people chaff at the SIEGE Engine mechanic, but personally I like the simplicity of it.

Dungeon Crawl Classics - If you like Gonzo unpredictable DnD with an old school feel look no further. Another system that I love. Very different feel than C&C.

While I still run a bunch of 5e it is for very select groups that buy into what I am going to run. I wont run the kitchen sink humans in skin suits DnD that seems to be expected by the unwashed masses. That said, I prefer C&C and DCC over 5e and run both depending on what type of game I want to run.

I'm playing on a VTT (Roll20) and all the nit-picky things that I didn't like about 5E seem to have been handled by the VTT (so far). Once this campaign is done I'll look into other options but my players are all over the country and Zoom/Facetime really didn't work well so I need a game supported well by VTT.

I am curious as WotC goes all in with their own VTT, if they continue to sell modules to competitor VTT.

Let's see...

The OP didn't include some obvious O5R options, such as Into the Unknown, Borderlands and Bugbears, etc. Basically, there are lots of games that try to blend OSR and 5e, many are good, many are free. There was a free one that was quite decent but I can't remember the name, it was recommended to me in this forum.

EDIT: it was Olde Swords Reign! Free, decent enough, with 5e and OSR inspiration.

Truth is, there are so many good ones out there for FREE - including the basic rules from D&D / SRD - that I'd avoid BUYING more stuff just to try a new but very similar system, although I do it sometimes.

I haven't tried these:

Tales of the Valiant
Level Up: Advanced 5th. Edition - a brief read indicates that this is unnecessarily complex, even more than 5e.
Nimble

13th. Age 2e - Looks decent for an "epic" version of D&D, PCs are very powerful
Cubicle 7 D20 (C7D20)
Pathfinder 2e - a brief read indicates that this is unnecessarily complex, even more than 5e.

Dragonbane - looks like a decent quasi-minimalist game

Castles & Crusades - a good OSr game, although I dislike the main engine. I wrote my impressions here:
https://methodsetmadness.blogspot.com/2023/09/a-few-thought-on-castles-crusades.html


Dungeon Crawl Classics - a great system if you're into tables, fun, gonzo. Not enough player options, IMO.
Hyperborea 3e - very good if you like AD&D. Review here:
https://methodsetmadness.blogspot.com/2024/04/hyperborea-players-manual-review.html

Worlds Without Number - another decent OSRish set of rules. enough player options.

Old School Essentials - one of the best B/X clones but not my favorite, others are described here:
https://methodsetmadness.blogspot.com/2023/01/a-glance-at-basic-d-bx-and-some-clones.html

I honestly think OSR is a different game than 5e. Yes you can try to emulate those elements in 5e, but 5e feels entirely different than any of the OSR flavors.

I don't have a solution to an alternate 5e other than asking - are you looking for new mechanics to play D&D Fantasy as a self-defined genre? If so, there's a ton of possibilities.

If you're looking for d20-specific systems, I'll always go with 1e/2e and modify them to taste.

If it's about D&D fantasy genre-emulation, and Pathfinder is a consideration - I'll always say "Go all the way and just go Savage Worlds Pathfinder, and use those rules for whatever setting you're currently wanting to play, and of course modify to taste.

Now I'm curious about this C7d20 (cubicle 7)

All I can find is about one year old or more.

I'm a bit curious just because I've read a few 5e alternatives. I don't even play 5e anymore, but I played a lot.

Given a choice between Shadow Dark and Olde Swords Reign, then I'll take Olde Swords Reign.

I like the customizable classes.  Normally only having the traditional four classes is boring to me.  But, this game customizations are big ones, letting you make Barbarians, Rangers, Paladins, and so on. 

It also simplifies down savings throws and skill checks by simply having a single number called a Proficiency Bonus.  A Cleric adds it when attacking when using a mace, or a warrior when making a constitution save throw for example.

And the best part, the rules are free.  The book is sold at cost, about $7.   

Just get it.