I also don't experience the extra cognitive load of choosing between languages when trying to express ideas, unless I'm trying to learn a new vocabulary word that I'm not familiar with. In specific, I can't relate to the commenter's point that: "When trying to think of a word, it comes to you in four different languages, which isn't helpful!"
As objective evidence, I use a software app called Glossika to practice listening and speaking to some extent, where the software plays a spoken English audio phrase and pauses before playing the translated audio. When I see the English for the phrase "The computer crashed" in Spanish track, the Spanish equivalent only comes to mind, and I don't simultaneously think of the French translation—even though I'm later asked to translate the same English phrase in the French track. At the start of each track, I have a certain context in mind (to make responses in a particular language), so I don't personally struggle with having to consciously focus to avoid mixing up words. In my experience, after at most ~20 seconds or so working in the target language, I say the right translations without any extra conscious effort of avoiding the usage of the wrong language.
The same goes for conversation practice. At the very worst—sometimes at the very start of a conversation—I can mix up a basic word. But after about less than a minute or so of speech, I'm think and express only in the language I'm practicing; I don't continually struggle with interference with other languages.
For my personal experience, studying both French and Spanish has even been beneficial for vocabulary acquisition. Learning that "le public" means audience in French made it a lot easier to shortly after remember that "el público" also means audience in Spanish. The sounds in French and Spanish are different, along with the words that typically surround new vocabulary words, so I don't personally struggle with choosing between different word options from different languages.
Speaking French and Spanish also has a separation due to the way that pronunciation physically feels. The back-of-the-throat guttural R in French especially feels and sounds a lot different than the Spanish trilled R with a vibrating tongue near the front teeth—so there is a barrier to mixing up French and Spanish words with these different sounds, as they "feel" very different to say in the mouth and throat. Spanish words also have a "stress" on the second-last syllable or syllable with a certain accent (e.g. Le envió for "I sent it to you" with a stress on the accented ió), whereas French has roughly equal stresses as a "syllable-timed" language [1], so the feelings of speaking the languages are very different, even if the vocabulary can be similar at a first glance.
In summary, I just can't relate at all to the idea of "juggling" between languages from practice with audio programs and conversation practice each week, though I recognize that different people have different experiences.
[1] https://ielanguages.com/french-stress.html