SM-A405FN with Exynos chipset? I am not aware of any emergency download mode. Let battery drain for few days. Press and keep holding both Volume buttons when plug in charger.
If you still can't reach download mode, buy JIG dongle (your last hope)
The notification "Keep the app open for taking the best and upload speed" is most likely shown by the app as there are a few known problems when apps running in background that could make the download stop so that the app has to resume (or even restart it if the server does not support resume) it which of course makes the download slower.
The main ...