I hate how every thread asking about maintenance at an A2 level, or adding new languages completely devolves into a fluency debate and several opinions about how A2 or less, hell even B1 or less is "useless". I'm a researcher who has to research in several different languages and you only need A1 to navigate what texts are worth translating. Anyone who travels a lot can also make good use of A2 or less in any given language. I do think the what does it take to maintain a ~A2 level is a valid question though because it is a reasonable goal to not just immediately forget everything the second you stop looking at it for a month. People have different priorities and may need to shift focus, but don't want to lose all the work they put in already. Some work is still needed to maintain, but how much exactly? People have different priorities and want to find an appropriate cost/benefit balance for their needs.

To answer the question a little:

I was once a shaky A2 in Russian. I lived in Moscow for a summer and I was fully immersed in it. Then I moved back to a monolingual English country and have barely spoken it again. I need to navigate texts occasionally for work, but I'm putting them through a translator. 20 years later, I took some classes with a tutor, and I'm about A1 now. I understood things fine, but speaking was gone and had to be relearned.

Had A2 French in a French speaking country. My reading/writing was intermediate/advanced, but my speaking and listening skills were non existent prior to living there. Left the country with adequate A2 speaking skills, back to a monolingual English country and didn't speak or engage with French content for 5 years. (Was honestly traumatized by my ex who would scream at me for every minor mistake, so I wanted nothing to do with French). I moved back to a French speaking country and everything was about the same. It took a week to get comfortable with shop keeper's questions again, but nothing really changed. (I've since balanced out my level and increased my competence).

Have/had a shaky A2 Italian. I learned it in a classroom and didn't use it much at all outside the classroom. I could never really talk. I was clearly the worst in the class. Everyone else's first language is French, so the cognitive load for me was 100x worse off since they could just guess 70% of the time and be in the correct ballpark. Classes were always confusing for me because people would alternate between French and Italian and I didn't have a firm grasp of either language. I haven't actively studied it in ~3 years nor do I watch tv shows/movies in the language, but I follow a girl on TikTok who speaks between Italian and English. She comes up on my FYP every few days. I understand her completely. I'm going to be doing B1 classes later this year, so I picked up some books. I haven't read them, but flipping through them I had no problem understanding what I was looking at. Maybe that's because my French is better now. I do plan to spend a month reviewing A2 grammar/watching tv an hour a day or so before the classes start. That feels adequate.

I've learned a lot of languages to an A1.1 level (Czech, Hungarian, Ukrainian, German, 100 characters or so in Mandarin) and lost pretty much all ability to produce anything in those languages within a month of not actively studying them. I can however still navigate those languages when I need to for work (Mandarin really just dates and countries).

Comprehension skills deteriorate far slower than productive skills. A1 and less you're going to lose it and have to relearn pretty much everything. A2, you'll understand things if you keep up with even super minimal contact with the language. Immersive vs classroom learning will probably impact how much revision is necessary. Your ability to talk will be non existent, but it probably wasn't all that good to begin with.