Good Linux plugins as a starting point

[sprnva]

In recent times there's a lot of focus on NAM profiles over circuit-level emulations. You can find various NAM loaders on the Guitarix GitHub. Ratatouille can load up to two profiles and follow them up with one or two cabinet IRs, with blend options for both. The downside with NAM loaders is the almost infinite amount of captures to go through.

On the modelled side, you could look at Arboreal Audio. They have one paid amp (OmniAmp) and a free one (STR-X). They're open source so you have the option to build OmniAmp for free, but buying it helps the developer.

Kazrog have a couple of amps and there's a couple of free amps here that require bringing your own cab IR.

[midi sentinel]

https://tonelib.net/ has some as well. I did not use them myself but they have been around for a while.