Here is the output
# btrfs su li /
ID 257 gen 88023 top level 5 path @
ID 258 gen 88024 top level 257 path var
ID 259 gen 87619 top level 257 path usr/local
ID 260 gen 87567 top level 257 path tmp
ID 261 gen 87238 top level 257 path srv
ID 262 gen 87931 top level 257 path root
ID 263 gen 87235 top level 257 path opt
ID 264 gen 87237 top level 257 path boot/grub2/x86_64-efi
ID 265 gen 87237 top level 257 path boot/grub2/i386-pc
ID 460 gen 87987 top level 257 path .snapshots
ID 461 gen 83043 top level 460 path .snapshots/1/snapshot
ID 462 gen 83043 top level 460 path .snapshots/2/snapshot
ID 463 gen 83043 top level 460 path .snapshots/3/snapshot
ID 501 gen 83043 top level 460 path .snapshots/41/snapshot
ID 504 gen 83043 top level 460 path .snapshots/44/snapshot
ID 509 gen 83043 top level 460 path .snapshots/45/snapshot
ID 518 gen 83073 top level 460 path .snapshots/52/snapshot
ID 523 gen 83073 top level 460 path .snapshots/57/snapshot
ID 538 gen 83073 top level 460 path .snapshots/72/snapshot
ID 541 gen 83380 top level 460 path .snapshots/75/snapshot
ID 551 gen 84135 top level 460 path .snapshots/85/snapshot
ID 567 gen 84804 top level 460 path .snapshots/100/snapshot
ID 568 gen 84805 top level 460 path .snapshots/101/snapshot
ID 569 gen 84808 top level 460 path .snapshots/102/snapshot
ID 570 gen 84809 top level 460 path .snapshots/103/snapshot
ID 577 gen 85712 top level 460 path .snapshots/110/snapshot
ID 598 gen 87212 top level 460 path .snapshots/131/snapshot
ID 599 gen 87308 top level 460 path .snapshots/132/snapshot
ID 600 gen 87352 top level 460 path .snapshots/133/snapshot
ID 601 gen 87354 top level 460 path .snapshots/134/snapshot
ID 602 gen 87358 top level 460 path .snapshots/135/snapshot
ID 603 gen 87359 top level 460 path .snapshots/136/snapshot
ID 604 gen 87408 top level 460 path .snapshots/137/snapshot
ID 605 gen 87503 top level 460 path .snapshots/138/snapshot
ID 606 gen 87642 top level 460 path .snapshots/139/snapshot
ID 607 gen 87713 top level 460 path .snapshots/140/snapshot
ID 608 gen 87730 top level 460 path .snapshots/141/snapshot
ID 609 gen 87765 top level 460 path .snapshots/142/snapshot
ID 610 gen 87848 top level 460 path .snapshots/143/snapshot
ID 611 gen 87902 top level 460 path .snapshots/144/snapshot
ID 612 gen 87928 top level 460 path .snapshots/145/snapshot
ID 613 gen 87931 top level 460 path .snapshots/146/snapshot
ID 614 gen 87986 top level 460 path .snapshots/147/snapshot
# btrfs su get-default /
ID 257 gen 88023 top level 5 path @
# cat /proc/mounts
sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
devtmpfs /dev devtmpfs rw,nosuid,size=4029828k,nr_inodes=1007457,mode=755 0 0
securityfs /sys/kernel/security securityfs rw,nosuid,nodev,noexec,relatime 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
devpts /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /run tmpfs rw,nosuid,nodev,mode=755 0 0
tmpfs /sys/fs/cgroup tmpfs ro,nosuid,nodev,noexec,mode=755 0 0
cgroup2 /sys/fs/cgroup/unified cgroup2 rw,nosuid,nodev,noexec,relatime,nsdelegate 0 0
cgroup /sys/fs/cgroup/systemd cgroup rw,nosuid,nodev,noexec,relatime,xattr,name=systemd 0 0
pstore /sys/fs/pstore pstore rw,nosuid,nodev,noexec,relatime 0 0
efivarfs /sys/firmware/efi/efivars efivarfs rw,nosuid,nodev,noexec,relatime 0 0
bpf /sys/fs/bpf bpf rw,nosuid,nodev,noexec,relatime,mode=700 0 0
cgroup /sys/fs/cgroup/memory cgroup rw,nosuid,nodev,noexec,relatime,memory 0 0
cgroup /sys/fs/cgroup/net_cls,net_prio cgroup rw,nosuid,nodev,noexec,relatime,net_cls,net_prio 0 0
cgroup /sys/fs/cgroup/cpu,cpuacct cgroup rw,nosuid,nodev,noexec,relatime,cpu,cpuacct 0 0
cgroup /sys/fs/cgroup/cpuset cgroup rw,nosuid,nodev,noexec,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,nosuid,nodev,noexec,relatime,blkio 0 0
cgroup /sys/fs/cgroup/freezer cgroup rw,nosuid,nodev,noexec,relatime,freezer 0 0
cgroup /sys/fs/cgroup/hugetlb cgroup rw,nosuid,nodev,noexec,relatime,hugetlb 0 0
cgroup /sys/fs/cgroup/pids cgroup rw,nosuid,nodev,noexec,relatime,pids 0 0
cgroup /sys/fs/cgroup/devices cgroup rw,nosuid,nodev,noexec,relatime,devices 0 0
cgroup /sys/fs/cgroup/perf_event cgroup rw,nosuid,nodev,noexec,relatime,perf_event 0 0
cgroup /sys/fs/cgroup/rdma cgroup rw,nosuid,nodev,noexec,relatime,rdma 0 0
/dev/sda6 / btrfs rw,relatime,ssd,space_cache,subvolid=257,subvol=/@ 0 0
systemd-1 /proc/sys/fs/binfmt_misc autofs rw,relatime,fd=30,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=2261 0 0
mqueue /dev/mqueue mqueue rw,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
hugetlbfs /dev/hugepages hugetlbfs rw,relatime,pagesize=2M 0 0
nfsd /proc/fs/nfsd nfsd rw,relatime 0 0
/dev/sda6 /var btrfs rw,relatime,ssd,space_cache,subvolid=258,subvol=/@/var 0 0
/dev/sda6 /boot/grub2/i386-pc btrfs rw,relatime,ssd,space_cache,subvolid=265,subvol=/@/boot/grub2/i386-pc 0 0
/dev/sda6 /root btrfs rw,relatime,ssd,space_cache,subvolid=262,subvol=/@/root 0 0
/dev/sda6 /opt btrfs rw,relatime,ssd,space_cache,subvolid=263,subvol=/@/opt 0 0
/dev/sda6 /usr/local btrfs rw,relatime,ssd,space_cache,subvolid=259,subvol=/@/usr/local 0 0
/dev/sda6 /boot/grub2/x86_64-efi btrfs rw,relatime,ssd,space_cache,subvolid=264,subvol=/@/boot/grub2/x86_64-efi 0 0
/dev/sda6 /srv btrfs rw,relatime,ssd,space_cache,subvolid=261,subvol=/@/srv 0 0
/dev/sda7 /boot/efi vfat rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 0
tmpfs /tmp tmpfs rw,nosuid,nodev 0 0
/dev/loop0 /snap/core/4917 squashfs ro,nodev,relatime 0 0
/dev/sdb6 /home ext4 rw,relatime,data=ordered 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
fusectl /sys/fs/fuse/connections fusectl rw,relatime 0 0
tmpfs /run/user/1000 tmpfs rw,nosuid,nodev,relatime,size=808532k,mode=700,uid=1000,gid=100 0 0
gvfsd-fuse /run/user/1000/gvfs fuse.gvfsd-fuse rw,nosuid,nodev,relatime,user_id=1000,group_id=100 0 0
tracefs /sys/kernel/debug/tracing tracefs rw,relatime 0 0