I could co-maintain as well.

@ChrisLane - Indeed, did it manually at first. Generated through makepkg now.

I'll add you to the co-maintainers, along with @whynothugo so this project can be maintained properly. If you want, you can of course take maintainer instead of just co.

@P67 I'm happy to help maintain or own.

Also, it looks like you might've updated .SRCINFO manually since it's not currently valid. Happy to fix for you but if not here's a diff:

diff --git a/.SRCINFO b/.SRCINFO
index d903194..2db63ea 100644
--- a/.SRCINFO
+++ b/.SRCINFO
@@ -4,6 +4,7 @@ pkgbase = aws-session-manager-plugin
    pkgrel = 1
    url = https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html
    arch = x86_64
+   arch = aarch64
    license = custom
    depends = aws-cli
    options = !strip
@@ -12,10 +13,9 @@ pkgbase = aws-session-manager-plugin
    backup = usr/sessionmanagerplugin/LICENSE
    backup = usr/sessionmanagerplugin/seelog.xml
    backup = usr/sessionmanagerplugin/VERSION
-   source_x86_64 = https://s3.amazonaws.com/session-manager-downloads/plugin/1.2.312.0/ubuntu_64bit/session-manager-plugin.deb
-   sha512sums_x86_64 = 0ee3978e197308395f85126ce9a59e427c50b0e3832cb2337b2ca29a687463b7238668e431e18b3a0be5dc9c278d5c9663cfb1d6fcdee5abc4673b900855c16a    
-   source_aarch64 = https://s3.amazonaws.com/session-manager-downloads/plugin/1.2.312.0/ubuntu_arm64/session-manager-plugin.deb
+   source_x86_64 = aws-session-manager-plugin-1.2.312.0.deb::https://s3.amazonaws.com/session-manager-downloads/plugin/1.2.312.0/ubuntu_64bit/session-manager-plugin.deb
+   sha512sums_x86_64 = 0ee3978e197308395f85126ce9a59e427c50b0e3832cb2337b2ca29a687463b7238668e431e18b3a0be5dc9c278d5c9663cfb1d6fcdee5abc4673b900855c16a
+   source_aarch64 = aws-session-manager-plugin-1.2.312.0-aarch64.deb::https://s3.amazonaws.com/session-manager-downloads/plugin/1.2.312.0/ubuntu_arm64/session-manager-plugin.deb
    sha512sums_aarch64 = fb07b660598ac5f6f765a040d2e1efa9b4df62e1b2558b1a259db21c6f53cafbb7ddf27262002156bad67b23da865e9181d972f6d57c7bd371d24cb5d899d7e6

 pkgname = aws-session-manager-plugin
-

I can help co-maintain this. I use it little, but use it on both x86_64 and aarch64.

I've updated the PKGBUILD to the new 1.2.312.0 version, including aarch64 support and also cleaned up Contributors/maintainers from the PKGBUILD contributor comments.

I am however no longer actively using ArchLinux (As a main machine, hence the slower updates.); if someone wishes to co-maintain or own the package, please step forward.

I can leave patches if anything breaks for it for me only on aarch64.

I personally cannot test aarch64 builds from build to install and functionality due to the sheer lack of having no system with this architecture in my possession.

I can however add it to supply this functionality based on the sums that are gotten from the files, if that's OK?

Sorry for the noise. This diff is more solid:

diff --git a/PKGBUILD b/PKGBUILD
index a0bd65b..1fbc2ba 100644
--- a/PKGBUILD
+++ b/PKGBUILD
@@ -6,14 +6,16 @@ pkgname=aws-session-manager-plugin
 pkgver=1.2.295.0
 pkgrel=1
 pkgdesc="AWS Session Manager Plugin for aws-cli."
-arch=('x86_64')
+arch=('x86_64' 'aarch64')
 url="https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html"
 license=('custom')
 depends=('aws-cli')
 backup=('usr/lib/systemd/system/session-manager-plugin.service' 'usr/sessionmanagerplugin/LICENSE' 'usr/sessionmanagerplugin/seelog.xml' 'usr/sessionmanagerplugin/VERSION')
 options=('!strip' '!emptydirs')
-source_x86_64=(https://s3.amazonaws.com/session-manager-downloads/plugin/${pkgver}/ubuntu_64bit/session-manager-plugin.deb)
+source_x86_64=(session-manager-plugin-x86_64.deb::https://s3.amazonaws.com/session-manager-downloads/plugin/${pkgver}/ubuntu_64bit/session-manager-plugin.deb)
+source_aarch64=(session-manager-plugin-aarch64.deb::https://s3.amazonaws.com/session-manager-downloads/plugin/${pkgver}/ubuntu_arm64/session-manager-plugin.deb)
 sha512sums_x86_64=('df1ef448487e5577a8c09d5de90c9a18628ee354ebfeb303565f97017e7ae0e61f380c2d330e858d7d334806b5fa2aae7c7fde16478c661590583a8c93115c5a')
+sha512sums_aarch64=('4fc12b0988a5d24e626476300d6be79b6720788ef043081540b01b58efd830153b79331064be7677c9f2c40501ec176da8a3ebedaf6c040de79b14033283de38')

I had to specify different names for both sources, otherwise tools like updpkgsums and some AUR helpers mix them up. This'll probably make updating the package in future more of a breeze too, since the filename won't collide for checksums any more.