I'm just trying to solve a common problem, but thanks to your explanations I realize that the diagnosis was always wrong.
The problem is not in the plugins.
Qtractor asks you where you host them and everything works.
Backing up plugins, and installables (if necessary) is logical.
This does not prevent portability or conservation over time.
The problem is in those plugins that are dependent on samples, mostly samplers.
And the solution is obvious: Don't use them.
If you have no choice but to use it because you want a very specific sound texture, this is going to be my work method from now on.
If you need a sampler, it's better to use an external tool than a plugin.
Launch the midi sequence from your project to the sampler.
Record the result as if it were a physical instrument.
Include a muted track with the samples used. You can add annotations to the name of each clip if needed.
If you open the project in the future, everything will sound as it should.
If you need to edit the midi sequence, you have the samplers to recreate the instrument. It doesn't matter if it's the same sampler you used or another one.
I think this should work.
I know it's a common problem, because there are samplers (for example Sitala) that have functions to search for lost samples. It's not a solution either, because there will be many samples with the same name and they will have completely different sounds.
So I'm sharing this conclusion in case it helps someone in the future.
Thanks to both of you for your help.
P.S.
In the case of library-based samplers (sf2, sfz...) I simply don't use them. As @windowsrefund pointed out, the size and complexity make them unmanageable.
It annoys me, because I have 3 irreplaceable pianos in sf2, and I can't invest in Pianoteq.
But from now on I'll only use gmsynth.lv2. By the way, it has recently been updated to "GeneralUser GS v2.0.1 by schristiancollins", and as I pointed out if you update some instruments they won't sound the same.
So... that mantra of updating everything isn't always convenient.
Not being able to manage different versions of a program as different programs was and will be a problem.
I'm just trying to solve a common problem, but thanks to your explanations I realize that the diagnosis was always wrong.
The problem is not in the plugins.
Qtractor asks you where you host them and everything works.
Backing up plugins, and installables (if necessary) is logical.
This does not prevent portability or conservation over time.
The problem is in those plugins that are dependent on samples, mostly samplers.
And the solution is obvious: Don't use them.
If you have no choice but to use it because you want a very specific sound texture, this is going to be my work method from now on.
If you need a sampler, it's better to use an external tool than a plugin.
Launch the midi sequence from your project to the sampler.
Record the result as if it were a physical instrument.
Include a muted track with the samples used. You can add annotations to the name of each clip if needed.
If you open the project in the future, everything will sound as it should.
If you need to edit the midi sequence, you have the samplers to recreate the instrument. It doesn't matter if it's the same sampler you used or another one.
I think this should work.
I know it's a common problem, because there are samplers (for example Sitala) that have functions to search for lost samples. It's not a solution either, because there will be many samples with the same name and they will have completely different sounds.
So I'm sharing this conclusion in case it helps someone in the future.
Thanks to both of you for your help.
P.S.
In the case of library-based samplers (sf2, sfz...) I simply don't use them. As @windowsrefund pointed out, the size and complexity make them unmanageable.
It annoys me, because I have 3 irreplaceable pianos in sf2, and I can't invest in Pianoteq.
But from now on I'll only use gmsynth.lv2. By the way, it has recently been updated to "GeneralUser GS v2.0.1 by schristiancollins", and as I pointed out if you update some instruments they won't sound the same.
So... that mantra of updating everything isn't always convenient.
Not being able to manage different versions of a program as different programs was and will be a problem.