I recently started a new character. I'm level 11. I've killed Mirmulnir but I do not absorb his soul. I get the message to investigate the body and I take all his stuff but he doesn't explode and let me absorb his soul. I've restored 3 times with the same lack of success. I don't see any bug listed on the wiki. I'm playing on a PC with a bunch of mods. Is it worth turning off all the mods and trying it?

can you post your load order?

the mod causing it probably is one of the ones that directly edit dragons

Not dragons directly, but some specific scripts. The cause is well-documented: another mod undoing changes that the Dragonborn DLC makes to dragonactorscript.pex and mqkilldragonscript.pex. Remove these from your Data/Scripts folder if you find them.

And still list your load order, since loose scripts may not be the cause. An incorrect load order (such as with USKP and UDGP which will cause the problem) or a mod that you either did not DL a Dragonborn DLC patch for or for whom the author doesn't even realize they've caused the dragon soul absorb bug may be to blame.

There was a bug with the Dragonborn DLC which seemed to block soul absorbtion on the first dragon, something to do with the same script used with Miraak's fight...

Anyway, if the unofficial patch doesn't fix it you can try disabling the problem script and loading a save before the first dragon fight eg.the auto save exiting whiterun.

data/scripts/MQKillDragonScript.pex

You'll just need to re-enable it for the miraak fight later. Just rename that script to disable it eg. MQKillDragonScript.pex.DISABLED

I deactivated all of my mods using Nexus Mod Manager. Played the game again and was able to absorb the soul. I want to reactivate the mods, but I'm not sure which the culprit might be. I can take a snapshot of my load order, but I'm not able to paste it into this posting and I don't see an option that would allow me to add an attachment. Is there an attachment option I'm missing.

My Redguard never absorbed Miramar's soul, he just left the lizard rotting in the plains of Whiterun. But that was on purpose; I wanted a non-Dragonborn character.

upload the pic and link it.

It's simple... you are not Dragonborn.