If it’s a private group (and not a channel) you can download them in bulk using the official telegram app.
Go to Settings -> advanced -> export telegram data (at the end). A pop-up window will appear that asks what data you want to export. Select only private groups and UNCHECK “only my messages” in order to download all chat history. Then you can select what data to download (photos, videos, voice messages, files, gifs…). Select the path where download the data and click export.
If it’s a private group (and not a channel) you can download them in bulk using the official telegram app.
Go to Settings -> advanced -> export telegram data (at the end). A pop-up window will appear that asks what data you want to export. Select only private groups and UNCHECK “only my messages” in order to download all chat history. Then you can select what data to download (photos, videos, voice messages, files, gifs…). Select the path where download the data and click export.