the ONLY explanation that makes sense in this text:

frais opposés "au réel" as opposed to the other type of "allowable business expenses" that are deducted from the taxable income "sur une base forfaitaire" (/ on a flat-rate basis) i.e. the "allowed deductions" for that type of business expenses are arbitrarily determined by the taxmen, with no regard to actually incurred expenses.

https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000039288050

Ces frais usuels font l'objet d'un forfait de 5 % des recettes brutes opposé aux auteurs ;
=>
this usual type of business expenses are accounted at a fixed flat rate of 5% of the gross revenues subjected to authors' rights (i.e. no need to produce any documentary evidence of what was really paid, it's simply "estimated" to be 5%, no matter if it's really more or less than 5%)

toutefois, s'agissant des œuvres des genres documentaire de création et adaptation audiovisuelle de spectacle vivant, les frais usuels afférents aux ventes d'un montant unitaire inférieur à 6 000 € (six mille euros) bruts font l'objet d'un forfait de 10 %.
=>
but "les œuvres des genres documentaire de création et adaptation audiovisuelle de spectacle vivant" are treated as a special case and for them the "allowable deductions for business expenses" are fixed at a (doubled) flat rate of 10%.


Autres frais opposés au réel :
=
other (business) expenses deductible in their real/effective amounts


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Note added at 2 days 1 hr (2021-08-20 16:31:09 GMT)
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here

"au réel" is the opposite of "taux / montants forfaitaires"

i.e. amounts really paid as opposed to amounts arbitrarily presumed by the taxman

from the whole text and from how the system of "(allowable) deductible expenses" works here "opposé(e)s" can only mean "what's in the opposite column in a system of double entry accounting" i.e. the "costs / expenses" that are on the opposite side of "revenues".

Or in practical terms: "costs / expenses" to be deducted from "revenues"


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Note added at 2 days 3 hrs (2021-08-20 18:06:55 GMT)
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correction - it's not about taxation but about paying royalties, although the calculations of the "base amount" are similar

The logic / the point of this story is about determining the amount that would be "the base amount" (/ "l'assiette") for the purpose of paying royalties to authors/artists.

According to this

... extension des avenants n° 1 et n° 2 à l'accord du 6 juillet 2017 entre auteurs et producteurs d'œuvres audiovisuelles relatif à la transparence des relations auteurs-producteurs et à la rémunération des auteurs du 17 avril 2019 [a kind-of "convention collective"]

the amount of "sales" on which royalties have to be paid is reduced by the amount of some "allowed deductions" - the logic being that these deducted costs have nothing to do with the author(s)/artist(s) and they shouldn't expect to get any "droits d'auteur" on that money.

Because it's child's play to artificially inflate these "costs" by creative accounting or careless spending (and/or to make it simple?), they (the parties to this "convention collective") have agreed to put a limit on the recognised amount of these "usual costs" in proportion to gross revenues.

see

Frais usuels opposés forfaitairement :


- frais de tirage des copies sur tous supports, frais d'encodage et transferts numériques ainsi que coût des supports, frais de mise en norme du cessionnaire des droits pour une exploitation France ou internationale ; frais de stockage et frais de vérification du matériel ;
- frais d'envoi numérique de fichiers, frais de transport du matériel, droits de douane ;
- frais usuels de promotion et de publicité du film (bandes démo, promotion, inscription marchés, brochures, photos, frais d'achat publicitaires, projections etc.) nécessaires à la promotion de l'œuvre concernée ;
- frais d'assurance, hors assurance Erreurs & Omissions (« E&O ») ;
- frais liés au recouvrement ;
- frais usuels de traduction ;
- tous les autres frais usuels, conformes aux politiques habituelles de frais de distribution et liés, notamment, aux évolutions économiques ou techniques propres à l'exploitation.

Ces frais usuels font l'objet d'un forfait de 5 % des recettes brutes opposé aux auteurs ; toutefois, s'agissant des œuvres des genres documentaire de création et adaptation audiovisuelle de spectacle vivant, les frais usuels afférents aux ventes d'un montant unitaire inférieur à 6 000 € (six mille euros) bruts font l'objet d'un forfait de 10 %.

OTOH, for some other "expenses" the really paid amounts are to be deducted - that's the part "Autres frais opposés au réel"

the costs under the 'Autres frais opposés au réel' heading have nothing to do with the making of an audiovisual product: they are indirect costs.

The opposite of indirect costs are direct costs, which vary with the REAL size of the audiovisual production.


What Is a Direct Cost?

A direct cost is a price that can be directly tied to the production of specific goods or services. A direct cost can be traced to the cost object, which can be a service, product, or department. Direct and indirect costs are the two major types of expenses or costs that companies can incur. Direct costs are often variable costs, meaning they fluctuate with production levels such as inventory. However, some costs, such as indirect costs are more difficult to assign to a specific product. Examples of indirect costs include depreciation and administrative expenses.

Source: https://www.investopedia.com/terms/d/directcost.asp