Joining Server 2008 Standard with AD LDS to Server 2019 AD DS with Domain Function Level 2008

So I have set up a New DC Server 2019 Datacenter with AD DS role installed and configured, accounts have been created for all users in the office, and a few are left to loin the Domain.

One of my concerns is that the one Server 2008 Standard is in a workgroup, running AD LDS. When I first joined this to the domain the DC was at Domain Function Level 2016, which caused a huge problem the Server was not operational after joining the 2008 Server to the domain. Had no backup and research did not help fix this issue. Rebuilt the server then rejoined the clients to the domain again, now coming to a few computers left is the one that started the problem, I think it was the Domain Function Level on the DC was set to 2016, when I have a 2008 Server in a workgroup and part of the error message was about server 2003 with service pack 3 installed. Lesson learned, now have a backup of the DC a Full backup for full bare metal restore if needed.

What if any issue would now come from joining this server to the domain? Can you join a 2008 Standard Server running AD LDS in a workgroup to a Domain DC, Server 2019 AD DS with Domain Function Level at 2008?

On a Server that has AD LDS running can you install AD DS and migrate AD LDS to AD? Then promote that to a BDC? Any suggestion would be helpful.

Just to be clear, The Server 2008 Standard running AD LDS is in a workgroup, The DC is Server 2019 with AD DS is the domain. Need to join the 2008 Server to the domain without breaking AD like I did last time. I was able to recover had to rebuild the rejoin to the network. I have it doing a full backup every day just in case I need it to restore. I did not set all of this up with I am in charge of setting up the domain and securing the network. This is one problem child I have to deal with.