Short answer: No, it isn't possible.
The Switch has a USB Type-C port that expects a very standardized communication protocol, including for devices to identify themselves, but even if you were able to create an adapter that pretends to be a USB device, neither the Switch nor the copy of the game are able to recognize the raw bytes sent by the GBA nor perform their end of the link-cable timing because they have no code to handle that type of interaction. Trade with link cables requires both systems to work together in precisely synchronized cycles as one of them generates a clock signal. It would be extremely difficult to create an adapter that is able to both provide the immediate hardware-level responses that the GBA wants while also providing the standard buffered USB communication that the Switch understands, not just due to extreme timing mismatches but also since the link cable uses its own proprietary protocol that would need to be reverse-engineered. Hypothetically, it may be physically possible if you were able to obtain full knowledge of the GBA and Switch's protocols, custom firmware on the Switch, and custom hardware to handle the interaction, but that's very unrealistic and I can't imagine that anyone would find it worthwhile for the level of effort.
The GBA Wireless Adapter won't work either because it also differs from standard modern wireless communication on pretty much every level. Motorola has reported that it uses the time division multiple access protocol, whereas the Switch uses Wi-Fi with various IEEE 802.11 protocol standards. Here's someone who tried it.
Creating a custom tool to translate between the two would be difficult since once again, the GBA's accessories are not only old but also proprietary and designed for very specific and unique functions, so they won't be the same as other TDMA devices and thus you don't necessarily know what you need to build to communicate with it. And again, the copy of FR/LG on the Switch does not have the same code as the copy on the GBA, so you also need to translate the game data for the modern copy. Timing issues are a problem again since the transfer speed on the GBA Wireless Adapter would be very slow by modern standards.
It is possible to send input information from the GBA to the Switch. I also don't see why it wouldn't be possible to have a tool that executes a series of steps where it dumps Pokemon data off the GBA, processes it, and then injects the same Pokemon into the Switch. The hard part is just to have the two copies be simultaneously tricked into thinking that they're actually using their respective built-in trade functions, which work totally differently and yet both demand immediate feedback and cooperation. As an analogy: even though you can get a translator to relay a message between two people who speak different languages, you can't get those two people to work together to sing a duet if they both want to sing different songs with totally different rhythms and lyrics.
Disclaimer that I am not an expert in hardware or network engineering, just presenting what I do understand about the situation.
